FOOTNOTES:
[12] The Plant, a Biography: M.J. Schleiden, p. 68.
[13] Because it had no root, it withered away. Mat. 13, 6.
[14] Du Breuil, Culture of Fruit Trees; English Translation.
[15] A.R. Whitney, Franklin Grove Nurseries, Lee Co., Ill.
CHAPTER IV.[ToC]
DWARFING.
DEFINITION OF—OBJECTS—EARLY FRUITAGE—DEFINITION OF TERMS. DWARFING STOCKS—OTHER MEANS OF DWARFING—DWARFS AND STANDARDS. PYRAMIDS OR CONICAL—ESPALIERS—LAYING BARE THE MAIN ROOTS IN SUMMER, TO DIMINISH THE VIGOR OF THE TREES—REMOVING A PORTION OF THEM—ROOT-PRUNING—TRANSPLANTING—EUROPEAN ESPALIERS AND WALL FRUITS—DU BREUIL'S CORDONS—CROWDING, AS A MEANS OF DWARFING—PINCHING, TWISTING, AND FRACTURE—FIELD'S PEAR HEDGES—OUR CLIMATE DOES NOT REQUIRE THESE MEANS OF TORTURE—FACILITY OF PROTECTION MAY RENDER THEM DESIRABLE—GENERAL INTRODUCTION OF QUINCE-DWARFED PEARS IN THIS COUNTRY—MANY FAILURES—SUCCESS DEPENDS UPON CARE—FRENCH SUCCESS—CHINESE—UNCONGENIAL STOCKS—IMPERFECT UNION—PINCHING—HIGHEST PERFECTION OF THE ART OF HORTICULTURE—EQUALIZE THE FLOW OF SAP—NATURALLY FLOWS TO HIGHER PARTS AT EXPENSE OF LOWER, MAY BE REGULATED BY TRIMMING—BY DISBUDDING—BENDING DOWN—PINCHING THE STRONGER, AND ENCOURAGING THE WEAKER—ILLUSTRATION IN THE STRAWBERRY—DWARFING THE APPLE—PARADISE STOCK—THE DOUCIN; UNFIT FOR ORCHARDS—ROOT-PRUNING—HOW IT OPERATES—TIME TO BEGIN—HOW TO BE PURSUED—SEASON FOR—EXPENSE—ROOT-PRUNING PLOW.
Dwarfing consists in so controlling the growth of plants as to reduce the natural size of any of our fruit trees, and bring them within comparatively narrow bounds. The objects of dwarfing are to enable us to plant a large number of specimen trees, or of varieties upon a small piece of ground, or to have small trees beside the alleys of our gardens. Such plants are also well adapted for growing in pots, or in the borders of an orchard-house. It is claimed for dwarfed trees, that they are more prolific than those which are worked on free stocks, which are often erroneously called standards, and it is also asserted that these dwarfed trees will bear sooner and produce finer and larger fruit.
The terms used may as well be explained at once. When we speak of dwarfing stocks, we mean such as are so uncongenial as to check the wood-growth; and thus, while producing smaller trees, they have a tendency to early fruitfulness if properly managed. But this condition may be superinduced by other means than these. Hence in speaking of dwarf pear trees, it does not follow that they have been worked on the quince or other uncongenial stock. A dwarf tree, of whatever kind, is simply one that has been caused to assume diminutive proportions. Dwarfing stocks are contrasted with free stocks, or those which would have attained the full size of the species, and which, when grafted, produce large trees. These are often mis-called standards, when contrasted with those that have been worked on the quince, or other dwarfing stock. Whereas, the trees propagated on free stocks, may also be dwarfed, by means that will be presently detailed; and the term standard refers really to the mode in which the training of the specimens has been performed. Those which are trimmed up as orchard trees are usually treated as standards, and are said to be trimmed to standard hight. Those branching at a lower point are called half standards. Those which are branched so low as to conceal the stem of the tree, and in which the limbs are so well managed that the lower ones are always the longest, and those above them gradually contracted to the point at the top, are called pyramids, or more properly conical trees. Whether dwarfed or not, trees may be trained in a variety of forms, such as the columnar, sometimes called the quenouille; the vase or goblet form may be given them, or the parasol shape, and they may be made to assume the form of a fan or other mode of extension laterally, when trained upon a wall or espalier frame, as may be seen in the illustrations given by Du Breuil; but it is seldom that our gardeners are willing to bestow the care and attention necessary to produce these results.
The vertical and oblique cordons represented and recommended by Du Breuil are very attractive, and admirable methods of training and dwarfing fruit trees, and of crowding a great many into a small space. His method of making an edging to the fruit-border with dwarf apples, inarched together so as to form a connected tree for its whole length, is a capital illustration of the control we may exercise upon vegetation.
Standards and pyramids are often trained as weeping trees, for the sake of gratifying the fancy of the cultivator, and with a view of bringing on that early productiveness which results from the check of the upward current of sap that is incident to such a mode of treatment. This is really a kind of dwarfing so far as it goes, and if commenced early in the life of the tree, it may become very effective, especially when combined with other means of reducing the growth. These are formed by arching the branches, tying their tips to a ring of wire or hoop secured near the ground, or simply by fastening weights to them sufficient to keep them in the desired position, and by tying the upper limbs to the lower ones. As is well known, the sap flows most readily toward the shoots that occupy a vertical line; it will be seen that its ascent will be seriously retarded in those that are bent, and their vigor will be diminished, and fruit-bearing will be promoted. This process must not be continued too perseveringly, lest the tree become exhausted by over-production.
Du Breuil recommends laying bare the principal roots of the tree in the spring of the year, so as to expose them for the most of their length, and leaving them in this condition during the summer. This exposure of roots to the sun and air diminishes the vigor of the tree, and hence it tends to the production of fruit. He also recommends the removal of a part of the roots in the spring, and replacing the earth; considering this a more energetic operation than the preceding, he advises caution, lest we injure the tree. This is simply root-pruning, a plan that has been pretty thoroughly tested in this country, where, perhaps, its beneficial effects are more needed than in any other, and where we shall even find it advantageous to have recourse to mechanical means for its performance in large orchards by horse-power, as will be set forth in another place.
A very successful method of obtaining the desired effect of dwarfing, which is early and abundant fruiting, consists in transplanting the trees in the autumn; this should be done very carefully, so as to preserve the roots from mutilation as much as possible. The effect of this will be to check the wood-growth the ensuing summer, and fruit-buds will be formed, for it is well known that these two opposite conditions of plant life are complementary the one to the other, and while we always desire to see them both proceeding together in a healthy tree, the wood-growth must have been moderated before we can expect to receive any fruit.
The French and English excel us in training upon walls and espaliers, and we may willingly yield them the palm; since, in this country, it is rarely necessary to incur so great expense for the production of good fruits, and as a means of dwarfing our trees, it is more expensive and requires more skill, care, and watchfulness, than other methods of producing this effect. Espalier training, however, affords the most beautiful opportunity for the illustration of many of the important principles of vegetable physiology, but it should never be undertaken by any one who is not familiar with these, and at the same time willing to exercise great patience and perseverance in their application to the subjects under his control. No blind pursuance of the abstract rules of the art can enable the mere routine gardener to become a successful grower of espalier trees. The modes of training are various, to suit the whims and necessities of the artist. Trees are fastened directly to the walls, or to trellises of wood or of iron, that are placed at a little distance from the masonry, or they may be entirely independent of any such structures, and exposed to the air and light freely on both sides. The trellises may be either vertical, or inclined. The limbs may be made to issue nearly opposite to one another, and be trained horizontally in two directions, with successive stages to the top of the wall or trellis, or they may be trained in a fan shape, with various modifications of what M. Du Breuil calls the palmette form. And a simple modification of this method of dwarfing may be made with some varieties of fruit, by training a single stem horizontally within a foot of the ground, as a border or edging between the path-ways and the cultivated ground.
The favorite method of training in France, at the present day, appears to be that called the cordon. This may be either the vertical or inclined. In this kind of espalier, the trees are dwarfed by crowding them closely together, and by successive pinching and other mutilation, such as bending and even breaking the shoots, which results in early productiveness. The trees are planted sixteen inches apart, and are trained to single stems, and so treated as to be furnished with the requisite number of fruit-spurs on their whole extent. This is quite a new application of principles, and one which is rudely imitated by Mr. Field's pear hedges, which, however, bear but little resemblance to the elegant cordons of Du Breuil beyond that of dwarfing by crowding and pinching. We are told that among the many advantages of this method, are the diminished time required to cover a wall or trellis with fruit, and the greater facility of replacing a dead or defective tree, which, in the usual espalier methods, is a very serious matter, requiring several years for its restoration and the production of a crop.
We are so blessed, in most parts of this country, with soil and climate that are well adapted to the production of fruit in the open field, upon sturdy orchard trees, that there is less necessity for introducing these elegant methods of pursuing the fine art of horticulture; and yet there are reasons in the uncertain climate of our winters, why these plans of training and dwarfing should be pursued by those who have the talent and the means for doing it. Until within a few years, there were not many dwarfed pear or apple trees in this country, and they were confined chiefly to French gardens and to the establishments of the wealthy. But since their more general introduction, immense numbers have been propagated and planted, and extensive orchards, particularly of dwarfed pears, have been set out with a view to profit. Some of these have been eminently successful, others are failures; the results will very much depend upon the amount of care which may be bestowed upon them.
The French have long practiced the dwarfing of certain varieties of fruits, and have been very successful in their results; but that wonderful people, the Chinese, excel all others in this branch of horticulture, for which they display a remarkable talent.
Dwarfing by Uncongenial Stocks.—The usual mode, which is literally a partial starvation of the tree by limiting the supplies of crude sap, consists in the use of uncongenial and dwarf-growing stocks, upon which the desired varieties are budded or grafted. These are, for the dwarfed pear, either Quinces, Thorns, the Mountain Ash, or the Amelanchiers; for the apple, the Paradise and the Doucin varieties of apple stocks; for the peach and plum, the Chickasas, or other dwarf plum stock may be used. The free-growing cherries are worked on the Mahaleb or the Morello varieties; but it must be confessed, that some of these do not produce a perfect dwarf without other treatment.
To produce a dwarf by grafting on an uncongenial stock, this should be so uncongenial as to form an imperfect union, which checks the downward circulation; the sap that has been elaborated by the organs of the scion is thus kept above the junction of the two woods, and, being so checked, the result is the early formation of fruit-buds, and a premature fruitage of the trees results in a direct proportion to the incompleteness of the union of scion and stock. This is often so very imperfect as to be very easily ruptured, the grafts are often broken out by a very small force being applied to them, sometimes even the weight of the fruit is sufficient to effect a separation, and an examination of the rupture will show how very slight or imperfect the union between the parts has been; in other cases, however, it is difficult to trace the fibres of wood-growth that belong respectively to the stock and to the scion, even when these have been so different as pear and quince, or plum and peach.
It is also considered desirable that the roots of the stock should be small and fibrous, and not long, naked, and straggling; the former will furnish the crude sap in more limited amounts, and are less likely to produce an excessively rampant or luxurious growth in the scion.
Many persons have been disappointed in the Mahaleb cherry, which has been reputed to be a dwarfing stock. It is found, that without the application of other means, the so-called dwarfed cherries grow as freely, at least in their early years, as those worked on the free stock, known as the Mazzard cherry. They will never make such large trees, however, and those who would enjoy dwarf cherry trees, should combine the different methods of producing the result.
By Pinching.—There are other means of producing the desired effects of dwarfing and early fruiting, which should be mentioned. These consist in systematic efforts to curtail the development of the wood-growth, by judicious pinching, of the tips or points of the branches, and to prevent the rambling of the roots by root-pruning. These it is designed now to examine. Pinching is practiced in the green-house with the happiest effects, and it results in the production of the most perfect form of the plants, and most abundant display of flowers. The constant check which is thus given to the wood system, causes the sap to seek new outlets, and instead of the one limb into which it had been flowing, and causing it to be developed; its flow is now directed to the other buds along its course, which presently burst out into lateral growths, none of which are so strong as the first, and these are induced to change the character of the buds so as to result in the production of flowers and fruit.
This system applied to fruit-trees has been most thoroughly carried out by the French, and is admirably described and illustrated by Du Breuil, in a work called Scientific Culture of Fruit Trees, and reproduced in our own language by Wm. Wardle, an English gardener and orchardist of high reputation.
It is not to be expected that in this country, where fruits are so easily produced, we shall soon reach such a point of horticultural practice as to lead us to the adoption of the European system of walls and espalier training, but we shall do well to watch the application of the very important principles involved in their practice, since these may be applied to our orchards with manifest advantage. In reference to the form and management of trained trees, it is established as an axiom that their permanency is dependent upon an equal diffusion of the sap being kept up throughout the whole extent of their branches. This occurs naturally in all trees, because they develop themselves in the forms natural to them, but in our gardens and orchards we make our trees assume unnatural forms. The sap flows to the highest parts by a law which is well known, though not so well understood; as a consequence, the lower branches do not receive their needed supplies, and being smothered by those above them, they eventually die and decay, leaving a naked stem supporting a top, or the common form of the natural tree. To maintain the shape we desire—be this the pyramid, the vase, or the espalier of whatever kind—certain operations must be performed from time to time, as the conditions of the tree may indicate.
Among these, Du Breuil advises to prune the strong branches short and allow the weaker ones to grow long, and thus to restore the balance. This may be done at the spring pruning, and also at any time during the growing season, when it may be necessary to check excessive growth at any one point: and upon this principle depends some of the most important practice of the summer pruning of our vineyards. The sap flows towards the leaves, and by removing them from one part, and leaving a preponderance upon another, we change the direction of its flow. As the strongest flow is toward those parts that are in a vertical direction, we may also check this tendency, or encourage it, by altering the position of the branch, as is done in the vineyard by tying up the canes we wish to have developed, and depressing the laterals with their fruit; so in a tree, we may depress the shoots which are too strong, and elevate those that are weak, to produce the desired effect. We may also greatly diminish the flow of sap to a strong branch by removing early all its useless buds; this is a sort of premature pinching to be sure, but when we consider the powerful influence exerted by these organs as centers of vitality, we can realize their attractive force in drawing the sap towards them. After the production of the full number of shoots upon the weaker branch, if the foliage continue to predominate upon the stronger shoot, it may be partially removed by early pinching, or cutting through the petioles, not by tearing them off; and as late as possible, remove the surplus and useless shoots from the weaker branches, which were at first needed to encourage the flow of sap in that direction.
The true pinching of the young laterals, or new shoots, should also be done as early as possible to keep them in check on the strong branches, while the same operation may be delayed on the weaker, from which we should remove only those that will be supernumeraries. M. Du Breuil also recommends the stimulation of the weaker limbs, by bathing all the green portions with a solution of sulphate of iron, made by dissolving twenty-four grains in a pint of water. This should be applied in the evening, when it is absorbed by the leaves, and acts as a powerful stimulant.
It is a well established principle, that the chief growth by extension will be made by the terminal bud, and this should either be removed by cutting back, or left upon the limb, according as we desire to grow our wood; if extension of the shoot be our leading object, all the lateral buds must be subordinated. So also, it is well known, that all circumstances, which retard the circulation, are followed by a diminution of the wood-growth, and by the development of flower buds.
The culture of the strawberry affords one of the best illustrations of the benefits and effects of pinching. The runners of this plant may be viewed in the light of wood-growth, or the increase of the plant by extension; even though these slender threads are not permanent, and they only serve to convey a bud to a distance from the parent plant, and place it under favorable circumstances for the formation of a natural layer. They are but annual productions, and hence there is no considerable deposit of woody matter, as in the limbs of trees, but they are thrown out from the parent plant just like woody branches, and are so much substance withdrawn from it, which, if retained or thrown back upon the plant, would have resulted in an enlargement of the main stem of the strawberry plant, and in the development of buds upon the crown, which become stored with the proper juices that result in the production of more abundant blossom buds. The result, however, is so admirable an illustration of this important element in the management of permanent and woody fruit-trees, that we may well look at an herbaceous plant, be it even so humble an individual as the prostrate earth-berry, as our ancestors called the delicious Fragaria.
DWARFING THE APPLE
Apples are generally dwarfed by working them upon the French Paradise stock, which is a very diminutive tree or bush, seldom rising more than a few feet high. This is the true stock for those who wish to indulge in the luxury of dwarf apple trees. Such are very appropriate for the small garden, or for the specimen grounds of a nursery establishment, and they sometimes make beautiful objects in the lawn or among the shrubbery, but they are wholly unsuited for orchard planting, as many a poor deluded purchaser has found out to his sorrow, a few years after having been beguiled by the smooth-spoken tree peddlers, who have sold many thousands through the country to farmers to plant as orchard trees.
There is a more vigorous stock which has been used for the same purpose, but it possesses much less dwarfing power. It is called the Doucin, or English dwarfing stock. This, however, exerts so little of the dwarfing influence, that at the end of eight or ten years the trees are generally about as large as those worked upon free stocks; but it happens unfortunately that early fruitage, the great object of dwarfing, is not attained by their use, for they will not have produced any more fruit than the common trees similarly treated.
By Root Pruning.—Among the many valuable hints which horticulturists have received, with the beautiful flowering and other plants, from our antipodes in the "Flowery Land," none has been of greater value than the practice of root-pruning. In this art of dwarfing even the large forest trees by mutilations of the roots and by other means, this curious people excel all others, as has frequently been stated. In Europe, and in this country also, root-pruning has been extensively practiced with the effect of partially dwarfing the trees, but more especially with the object of inducing prematurely the fruitfulness we so much desire, and which is a natural result of the diminished supplies of crude sap furnished by the contracted roots of a tree that has been treated in this manner. The balance between the wood-growth by extension, and that which results in fruitful spurs is sooner established, and the sap is directed to the formation and support of the fruit.
We should not commence the application of this severe treatment until our trees have been allowed to establish themselves firmly in their stations, unless we desire at the same time to produce decided dwarfs by means of root-pruning. In this case the treatment may be commenced in the nursery itself; the stocks should be transplanted once or oftener before being worked, and the young trees should be moved annually, which will so shorten the roots as to make them a mass of fibres, occupying the whole soil close about their main divisions, and the subsequent removals can then be easily effected, with but a slight check to the tree, which becomes furnished with fruit spurs at a very early period of its existence, instead of its requiring years to reach its natural period of fruitfulness, as is the case with some varieties, particularly of the pear.
As generally practiced, however, root-pruning is postponed until the trees have made a free and vigorous growth, and have become well established in their stations. Then if the growth be too vigorous, and there do not appear any indications of the formation of fruit spurs, as is often the case in the fertile soils of the West, our impatient orchardists complain of the barrenness of their trees, and seek a remedy in root-pruning. This is generally performed with a sharp spade, with which a trench is dug in a circle around the tree. The excavation should be deep enough to reach all of the lateral roots; these are generally within a foot of the surface. The ditch need not be much wider than the spade, and the soil can be thrown back at once, but all the roots should be severed, if we desire to produce the effect of checking the wood-growth. The diameter of this circle will depend upon the size and vigor of the tree to be operated upon. As a general rule, it may be made in the proportion of one foot to each inch of the tree's diameter. The work may be done at any time after the spring growth has begun to harden, or during the autumn and winter, and until the buds are about to break in the spring. The operation is wonderfully conducive to the end we have in view, and we often see a vigorously growing but barren subject, transformed in a single season into a fruitful tree, covered with blossom-bearing spurs that are full of promise of delicious fruits. In some varieties, however, these fruit spurs require more than a single season for their perfection.
Now it may be objected that this labor will be expensive, and so it is, as all hard work with the spade must be; but what of that, when we consider the happy results that ensue in golden harvests. But it has been suggested that this labor may be performed by farm machinery, using a strong plow, or rather a sharp cutter attached to a plow beam, and drawn by a powerful team at the requisite distance on either side of the rows of trees, and in directions crossing each other at right angles. This, of course, like all mere mechanical applications, must be uniform, whether the necessities of the trees be equal or not; whereas, by hand-labor, we may vary the distance at which the roots are to be cut, according to the vigor and size of the trees demanding the treatment.
This topic will be again referred to in the chapter on Pruning, where also it will be necessary to recur to the subject of Training, which was incidentally alluded to in connection with Dwarfing.
CHAPTER V.[ToC]
DISEASES.
DIFFICULTIES IN THE OUTSET—WHAT CONSTITUTES DISEASED ACTION—NO ANALOGY TO ANIMAL SICKNESSES—CONGENITAL DEFECTS—DEBILITY. DEFICIENT STRENGTH OF FIBRES—DEFECTIVE FOLIAGE—IMPERFECT AND REDUNDANT BLOSSOMS—THE CIVILIZED AND CULTIVATED PLANT MAY BE ABNORMAL ALTOGETHER—UNSATISFACTORY ACCOUNTS OF DISEASES IN PLANTS—LANKESTER'S CLASSIFICATION CONSIDERED—EFFECTS OF THE EXCESS OR PAUCITY OF MOISTURE, HEAT, AND LIGHT—MODE OF ACTION OF FROST—INJURY RATHER REFERRIBLE TO THE CONDITION OF THE CIRCULATION THAN TO THE DEGREE OF COLD IN MANY HARDY PLANTS—INFLUENCE OF THE SOIL—LIGHT THE GREAT STIMULUS, ITS WITHDRAWAL SUSPENDS HEALTHY ACTION—ITS SUDDEN RESTORATION CAUSES DEATH BY SUN SCALD—INJURY BY SUNSHINE IN WINTER—POISONOUS GASES—MIASMATA—POISONS IN THE SOIL—PARASITIC PLANTS, EPIPHITES, FUNGI, PEAR BLIGHT—VARIOUS THEORIES—WHAT WE KNOW, AND WHAT WE DON'T KNOW—TREATMENT—ROOT PRUNING SUGGESTED—SATISFACTORY RESULTS—MILDEW BLIGHT IN PEACH AND APPLE—TWIG BLIGHT IN APPLE AND QUINCE—THE APPLE BLIGHT—BITTER ROT—CRACKED FRUIT—SCAB—MILDEWS—KIRTLAND'S VIEWS AND SUGGESTED REMEDY—WOUNDS AND INSECTS—NEEDING THE AID OF SURGERY RATHER THAN MEDICINE—DESTRUCTION OF FOLIAGE BY INSECTS IMPAIRS THE HEALTHY CONDITION OF THE PLANT—RESUME—SELECT HEALTHY TREES OF HEALTHY VARIETIES—EMPIRICAL CHARACTER OF TREATMENT USUALLY RECOMMENDED FOR DISEASED TREES—THE BLACK KNOT—THE ROT AND MILDEW OF THE GRAPE.
In opening a discussion upon the nosology of vegetation, it may be expected that one who had spent many years of his life in the investigation of the diseases of the human family, and at the same time was something of a student of comparative anatomy and physiology, tracing analogies between the animal and vegetable kingdoms, should be familiar also with the diseases of plants. Such an anticipation, it is feared, will not, in the present instance, be realized. Indeed, the writer feels very much at a loss how to proceed in discussing this branch of the subject, and hardly knows what departures from undoubted health and vigor should be considered worthy of the title of disease. Nor is it easy to trace the causes of the conditions that are generally viewed in the light of maladies. We find the manifestations both in the tree or plant, and in its several parts, and also in the products which chiefly interest us; the fruits themselves, are often deteriorated by what is called diseased action of different kinds. The analogy to diseases of animals is certainly not very distinct. We do not find anything like fevers, or gout, or rheumatism, in plants, but we may consider some of their conditions somewhat in the light of dropsies, and plethora or hypertrophy on the one hand, and of anæmia or atrophy upon the other; we may consider canker and the death of some parts of a plant analogous to gangrene, and mortification in the animal subject. Then again we find congenital defects in individuals among plants, just as we do among animals. Some are always less vigorous than others, and thus certain varieties seem possessed of a degree of inherent disease that perpetually prevents them from displaying the requisite strength and vigor which we so much desire in our plantations. Certain varieties that, from the size and excellence of their fruits, have attracted the attention of pomologists, are so deficient in health and vigor as to be considered diseased, and are therefore very properly condemned as unworthy a place in our orchards and gardens; others appear simply deficient in the production of some one part, as is illustrated by the inferior strength of the woody fibres of some trees, which break easily under the weight of their own fruit, and thus destroy the symmetry of the tree and diminish its productiveness. Others have defective foliage, which is attended by the imperfect performance of the functions of growth, both in the fruit and in the sustaining woody fibres; others again produce defective blossoms with either a redundancy or deficiency of the parts that are necessary for the production of the seeds needed for the perpetuation of the species. When the parts are deficient, the flowers are called barren or infertile. A redundancy or multiplication of parts is seen in double flowers of our gardens, where they are much prized for their beauty, though considered monstrosities by the botanist, and perhaps properly referred to diseased action by the nosologist.
It is evident, that very often the conditions of a plant and its products, which we most highly prize, and towards which all our efforts in its culture are directed, are really departures from the natural and healthful status; in other words, what we covet, is really a state of diseased and abnormal action. With the other secondary objects of occupying and ornamenting the barren wastes of the earth with plants, and thus supplying food to hosts of insects, and to the higher animals, nature also has primarily in view, the production of perfect seeds for the perpetuation of their species, by the plants that are profusely scattered over the globe. Man, on the contrary, often rejects the true seeds as worthless when compared to their juicy fleshy envelopes that constitute his favorite fruits, or the enlarged and succulent roots, tubers, stalks, and leaves, that characterize his garden vegetables and field crops; while in the grains proper he seeks sustenance in the true seeds, which become the object of his greatest care and ingenuity to enlarge, to increase, and to develop, particularly in regard to their nutritive qualities.
Most writers upon the diseases of plants have given us very indistinct notions upon the subject, and have done very little to enlighten their readers; while they have written voluminously upon the unhealthy and unsatisfactory condition of certain vegetables, and have given us most extensive accounts of the treatment by which they propose to remedy the evils complained of, we gather little of the information needed to enable us to understand the true state of the case, or of the causes of the disease, if it is to be considered such. The reader need not expect that he will be more enlightened by this chapter than he has been by the essays to which reference is here made, but he will be led to a consideration of some of the causes of those departures from health and vigor which are considered diseased action, and in this way he may possibly be put upon the track which will lead him to the avoidance of disastrous results. More than this will not be attempted.
Perhaps the most satisfactory account of diseases of plants is that given by Lankester, in which he divides them according to their causes, as follows:
1st—Those produced by changes in the external conditions of life, such as redundancy or deficiency of the ingredients of soil, of light, of heat, air, and moisture.
2d—Those produced by poisonous agencies, as by injurious gases, miasmata in the air, or by poisons in the soil.
3d—Those arising from the growth of parasitic plants, such as the various Fungi, Dodder, Mistletoe, etc.
4th—Such as are caused by mechanical injuries or wounds, and by the attacks of insects.
These may be considered separately: 1st—It may be assumed, and has been already well established by botanists, that every plant has its own peculiar constitution, adapting it to certain atmospheric conditions, and that for its healthful and successful culture, these must be understood and adhered to, within comparatively narrow limits. Tropical plants, as is well known, cannot be cultivated beyond their natural limits, except under circumstances where their natural conditions are nearly imitated by the gardener; and even in our stoves and hot-houses, these plants do not compare in vigor with their fellows that luxuriate in the hot and steaming atmosphere of the tropics, under the stronger light of such a clime as is natural to them. On the contrary, the plants of northern latitudes will not grow and produce seeds where temperature is too elevated. Those from a humid atmosphere suffer in an arid clime, and those which thrive in dry sandy regions suffer equally when introduced into a humid atmosphere.
Thus we find, that where there is too much moisture for some of our cultivated plants, they are inclined to be too succulent, and this very excess may produce a dropsical condition that is really a state of disease. Thus we suffer in a loss of fruit, which will fall badly before its period of maturity, and that which remains its full time is found to be thin and watery, deficient in the high spicy aromatic flavor which is so highly appreciated by the connoisseur of these choice products. When, on the other hand, the arid character of the soil and climate prevail to an extent that is uncongenial to any particular fruit, we shall find that its growth is arrested, and that its highest qualities are not adequately developed: this is frequently observed in an unusually dry season—and in California, where irrigation is required to enable the orchardist to produce some of the succulent fruits, the most remarkable size and beauty have been attained, but we are told that it was often at the expense of the desired flavor that the same varieties acquire, under circumstances more advantageous to the development of their superior qualities.
So in many of our fruits, the successful results depend upon the hygrometric condition of the atmosphere, and Liebig suggests that a very prolific source of diseased action in plants, arises from the suppressed evaporation and transpiration consequent upon such atmospheric conditions.
Too much moisture prevailing at the time of the blossoming of our fruits, especially moisture precipitated in the form of rain during this period, is sometimes disastrous to our crops, both of cereals and of orchard fruits. Continuous showers prevent the development of the pollen-grains, and their transfer to the stigmas of the blossoms, so that the fruit does not set well. Fortunately this does not often occur in our glorious climate, which is so highly favored by an abundance of light and sunshine, which are the great and essential stimuli of the higher orders of plants. The loss of our fruit crops in some parts of the Ohio Valley in the years 1862, 1865, and 1866, was fairly attributed to this cause.
We must not overlook the unhealthy influences produced by an excess of moisture in the earth. Many plants that naturally delight in a dry porous soil, become weak, unfruitful, or even seriously diseased when they are planted in low wet grounds, or upon such as are underlaid by a very tenacious sub-soil, while an opposite condition is equally unfavorably to those that are naturally more aquatic in their tastes and habits. In the former case we learn to avoid such soils and situations, unless we are able to change their character in this respect by thorough under-draining, which will completely remove the evil, and the remedy becomes merely a question of expense.
A certain amount of temperature may be assumed as requisite to every plant, or rather it may be affirmed that some plants cannot exist and thrive except within a certain range, and it has been asserted that each class of plants requires a mean temperature for the year that shall not vary many degrees: the range of this variation has perhaps never been satisfactorily ascertained. But it is well known, that both heat and frost act injuriously upon vegetation. Mr. Lindley tells us that "the extreme limits of temperature which vegetables are capable of bearing, without destruction of their vitality, have not been determined with precision." When the temperature is maintained at a higher point than is natural, the plant is excited to undue activity of growth; but this is attended with an enfeebled condition, often seen in badly managed green-houses. Mr. Knight found that certain plants were rendered abortive by the production of male flowers only, when exposed to too great heat, and by an opposite treatment, when subjected to a low temperature for a long time, others produced only female flowers. In some plants a high degree of heat, with moisture, results in the production of leaves only, and Humboldt found that wheat was grown about Xalapa, Mexico, as a fodder plant, because it produced an abundance of grass, but did not form ears nor grain.
A diminished temperature, on the contrary, removes the stimulus of growth, and leads to the suspension of all vital action in proportion to its reduction. At the freezing point it is probable that all such action ceases, though in this regard there is great difference among plants; the mosses and lichens will flourish, and the Chickweed will vegetate and blossom at a temperature very little above freezing. The access of frost, after vegetation has somewhat advanced, often proves very disastrous, and we not unfrequently lose our crops of fruit by such an occurrence during the period of blossoming, or even afterward.
Some plants in a dormant condition, will endure uninjured a great depression of temperature, while others will be destroyed by the slightest approach of frost. According to De Candolle, this may depend upon the greater or less amount of water they contain, upon the greater or less viscidity of their fluids, or the rapidity with which these fluids circulate. Those with larger cells he thinks most easily injured by frost, and those which contain a great deal of air are able to resist it best. The freezing point will vary according to the quality of the sap, for we know that different vegetable juices congeal at different temperatures. The manner in which cold acts upon plants depends upon their physical structure. Lindley says, freezing is attended with the following effects:—The fluids contained within the cells of tissue are congealed and expanded—this produces a laceration of the cell-walls, and impairs excitability by the unnatural extension to which the cells are subjected; the air is expelled from the air-vessels and introduced into parts naturally intended to contain only fluid; the green coloring matter and other secretions are decomposed, and the vital fluid or latex is destroyed, and the action of its vessels is paralyzed. The interior of the tubes, in which fluid is conveyed, is obstructed by a thickening of their sides. So we have as a result, both mechanical, chemical, and vital changes.[16]
Our hardy fruit trees are woody perennials that hybernate during the winter. Yet we find that even these suffer upon some occasions from a great depression of temperature; it has been asserted that a certain degree of cold would inevitably destroy the blossom buds at least, and we often find that the bark is burst off from the wood, and in some instances the wood itself is so injured as to suffer from a kind of decomposition, and to become affected with a change generally known as the dry rot, losing its elasticity and hardness, and acquiring a whitish color, which is supposed may arise from the introduction of the mycelia of fungous growths. Now it is believed that these injuries do not arise so directly from the degree of cold to which the tree has been exposed, as to the condition of its circulation at the time of the exposure. If the sap have been excited by mild or warm weather, as is so apt to be the case in our changeable climate, the sudden depression of temperature will produce disastrous effects, even when the cold has not been very severe. This is manifested by the bursting of the bark in young trees in the early part of winter, while they are yet holding their leaves, and of course having a circulation somewhat active. Hence the importance, now very well understood by our nurserymen, of checking the growth of young trees in time to have their terminal buds thoroughly ripened before the approach of frost. This, to a certain extent, is subject to our control; but we cannot foresee the character of the seasons upon which the safety of our orchard trees will, in a great measure, depend, and they are less easily managed. When the autumn is dry, and continued late into winter, as sometimes happens, we see a perfect ripening of the wood, with a great development of blossom buds, and then we may confidently calculate upon the safety of our fruits, provided they be not exposed to a warm period at mid-winter, that shall excite some activity in their circulation, which would suffer terribly from any sudden and great depression of temperature such as frequently occurs, carrying the mercury from summer heat to a point below zero, in a few hours. Such a change has amounted to 68 degrees in nine hours.[17]
The influence exerted by the soil upon the healthiness or unhealthiness of our trees has already been alluded to incidentally, but it is an important subject of inquiry whether this may arise from a redundancy or a paucity of some particular ingredients necessary to sustain the plants we desire to cultivate. Liebig has pointed out how chemistry may be brought to our assistance in solving such a question. As all the inorganic elements found in a tree and its fruits, must have been derived from the soil in which it grew, he suggested that the ashes of the plant would show us exactly what it needed, and then an examination of the soils would inform us whether they contained all the necessary elements, and in the right proportion. Hence arose the doctrine and the practice of applying special manures, which has been so fashionable in our day. Though there be many doubters as to the efficacy of such investigations and practices, most sensible and enlightened agriculturists admit the truths which Liebig has propounded.
Light is the great stimulus of vegetation, an essential element to its existence: its withdrawal is followed by an arrest of some of the most important functions of vitality, and yet we find that there is a great difference among different species, as to their requirements of this element, and also that various parts and several products of vegetation require very different degrees of light for their perfection. It is also found that a sudden exposure of parts from which it had been withheld, is often attended with disastrous consequences. Its withdrawal does not so immediately destroy the plant, being attended with the etiolation of the parts that are usually colored, but a sudden re-exposure to the sun's rays will now destroy the plant. So the removal of a portion of the foliage from a tree, or the exposure of the bare stem of one that had been previously sheltered, is often attended with severe effects, known as sun-scald—for which there is no remedy, but very easy modes of prevention. The best of these is to provide against the evil by reserving the lower branches to shade the stem. There are other excellent reasons for this practice, which will be brought forward in the chapter on Pruning.
Frequently, however, the nurseryman, or perhaps the injudicious efforts of the planter himself, may have removed all the side branches of the young tree, and as these cannot be replaced, we may substitute for them a shelter from the scorching sun to which the newly planted tree is exposed. This may be done by tacking two narrow boards together at their edges, like a gutter spout, and setting them upright on the south side of the tree to shade it. A wisp of straw, tied loosely to the stem, will answer a very good purpose; but both of these appliances are objectionable, because they furnish a shelter for insects, and thus they fall short of the natural shading of the stem by the foliage of its own branches.
It is not only the scorching suns of summer that damage our young trees that are thus exposed by injudicious trimming. Even the bright rays of a mid-winter sun, falling upon the frozen stem, will often effect the most serious damage, and should be guarded against with equal care; but here the natural protection will answer, for the shade of the naked spray of the laterals is found all-sufficient in the well-trained tree.
2d—To resume the consideration of Lankester's causes of disease, it must be admitted that some diseased conditions may be produced by poisonous gases, but the usual result will be the death of plants confined in such an atmosphere. The natural power of diffusion of all gases among one another in the open air, prevents the danger that would ensue in a confined situation. The accidental production of sulphurous and other poisonous gas, or the escape of smoke from the flues or from the tobacco-pan in the green-house, sometimes produces the most disastrous effects upon the plants subjected to their action. So, in crowded cities, it often happens that the effects of coal smoke and other gases, generated in the furnaces and manufactories, are very injurious to vegetation. The coal soot falls in flakes like lamp-black, which covers the surface and obstructs the transpiration of the stomata, and thus seriously affects the health of plants in such situations.
The action of miasmata, suggested by Lankester, is as obscure in the effects produced upon plants as in those upon animals. The presence of these atmospheric conditions cannot be detected by any of our tests, nor can their effects be prevented by any means in our power; we know little or nothing about their characters, yet we cannot deny their existence: finally, they serve as a very convenient explanation, though a very unsatisfactory one, for the incursions of maladies that are of an obscure or unknown character. Whether of a miasmatic nature or not, no one can deny the existence of certain atmospheric conditions, which appear to produce disastrous effects upon some of our vegetable productions whether these be inherent to the air itself, or are only conveyed by it from one place to another. The inexplicable potato disease may owe its origin and diffusion to such a cause, and the grape malady, which appears to be dependent upon atmospheric causes, may at least be carried from one vine to another upon this medium, in the form of the minute spores or seeds of the fungi that are believed to be the cause of the trouble.[18]
Poisons in the soil are frequently very deleterious to vegetation, and we often find extensive injuries to our plants produced by this class of agents. When these are of a chemical nature, as is usually the case, they may be satisfactorily treated by applications that will neutralize their effects. In cities the escape of the illuminating gas, that is carried in subterranean pipes, has often so poisoned the soil as to destroy the shade trees by the side of the streets.
An excess of certain saline and alkaline ingredients often produces barrenness in the soil, by a sort of poisoning, even with those articles that in smaller quantities are used as manures with the happiest effects.
3d—The influence exerted upon vegetation by the growth of parasitic plants, cannot be observed without forcing us to the conclusion that they are prejudicial to the health of the plants they infest—since they either cover and smother the foliage by twining upon it, as is the case with the Dodder; or fasten themselves upon a limb, appropriating the sap that was intended for its support, and thus starve it, as does the Mistletoe; or attaching themselves to the bark, they interfere with its functions, as is done by the lichens and mosses; or, following the descending scale, in the size of these parasites, but meeting in them foes of much greater importance, we find the minute but innumerable fungi attacking the wood, the bark, the foliage, and the fruits, of our gardens and orchards, and committing incalculable damage—thus entailing serious disease. A very important question has arisen, however, as to whether the inroads of fungi were the cause or the consequence only of disease. A question which it will be necessary to leave to wiser heads, only observing that these epiphytes do appear, under certain atmospheric conditions, to invade some plants that had previously seemed to be in perfect health. That they are transported upon the air, in the form of very minute sporules, is unquestioned, and that their growth is dependent upon certain atmospheric conditions, is equally admitted, but whether they induce disease, or are only able to take possession of a plant that is not in a perfectly healthy condition, does not yet appear so clear. The very eminent Mr. Solly is of the opinion, that in the potato at least, the existence of parasitic fungi is a secondary result of previous disease. So it may be with our fruits, and there is considerable testimony to favor such a belief in many cases, where we find, with the appearance of these fungi, other causes of unhealthiness.
The leaves of the apple trees in some seasons become coated with a black efflorescence, that gives the tree a very sombre appearance, and seems to affect its health. I am not aware that any one has yet made any microscopical investigations of this condition of the foliage, which looks as though it were dusted with coal-smoke. It has been supposed, however, to be the result of a fungous growth.
Pear Blight.—This is a subject upon which so much has been said and written, that any one may well shrink from its discussion. The condition in which the invasion of the malady finds the tree has been pretty thoroughly ascertained, and the sad state in which it is left after the attack, is too well known to need any learned description. It is well called the blight, for nothing short of scorching by fire can more effectually destroy the life of the tree and blight our hopes of its usefulness. The varied theories and suggestions that have been advanced in attempted explanation of this state of things are altogether unsatisfactory so that it may be said we know nothing about the disease, nor whether it be occasioned by frozen sap, by fungous invasion, or by insect attacks, all of which have been set forward as causes of the difficulty. None of these explanations have been clearly proved, and they seem rather guesses than established facts in the history of the disease, which breaks out in the midst of the season of growth, and attacks those trees that are in the midst of the most vigorous production of succulent shoots; but it is not confined to the young wood; on the contrary, it appears first in the hard bark of limbs, that are two or more years old. This turns brown, becomes desiccated, and thus the circulation is arrested, and the foliage as well as the bark is affected. The outer extremities of the leaves wilt, die, and turn suddenly brown and then black, and often remain adhering by their petioles for months—sad testimonials of the destruction caused by the blight. The disease appears to extend in some instances, but it is not proved that there is any poisonous matter generated by a blighted limb that could have entered the circulation, and then have been transmitted to other parts of the tree. The apparent extension of the disease is rather believed to have been the successive development of the trouble from different foci, which had successively invaded so much of the bark as to have more or less completely arrested the flow of the sap. In some limbs of small size, a patch of dead tissue of moderate dimensions would entirely arrest healthy action early in the season, and destroy the portion of the branch beyond it; in other branches of greater size, quite a large patch of the dead bark might exist for a long time without entirely surrounding them, and arresting the circulation, which would thus be kept up until a later period, when at length this occurred, the symptoms of blight would appear.
The treatment of this malady is quite unsatisfactory, and gives us no clue to the cause of the trouble. Various plans have been suggested, the most satisfactory is the removal of the affected limbs—not that it cures the disease, but because it takes from us the sad mementos of our loss. We have been advised to pare away the diseased portion of old bark with a spoke-shave, or some similar instrument; but it is apprehended that few persons would ever find this patch of dead bark until they have the fatal evidence of the blighted foliage, and no possible good can result from its removal at that time.
This trouble is connected, in many instances, with an excessively vigorous growth of shoots; indeed, some of those varieties which are most thrifty, suffer the most, while those which make firm and moderately short shoots, seldom blight. Hence it has been inferred by some, that if we can check this excessive vigor, and reduce the wood growth to a moderate amount, not exceeding ten or twelve inches, annual extension, we shall be able to prevent the occurrence of blight. This object is easily attained by root-pruning the trees severely in the spring of the year. So far, we can only say that trees so treated, have not blighted; but it does not follow that they would have suffered if let alone.
Another form of blight may often be seen in the peach and in the apple; it consists in a loss of vitality of small twigs and their foliage in several parts of the tree, especially in the inner portions that are not freely exposed to the air and light. In the peach, this disease is accompanied with the decay of the fruit upon these twigs, which rots and becomes moldy. This trouble is usually attributed to mildew, and it is probably owing to some form of fungus invasion.
Quite a different affection of the twigs is that known as the "blight" in apples and quinces. This attacks only the young shoots of the current season's growth, which suddenly wither and become brown at mid-summer. The same condition occurs also in the shoots of the Italian mulberry. The cause of this malady is not very apparent; by some persons it is attributed to the punctures of minute insects, but they have escaped the scrutiny of other observers, who attribute this blight to atmospheric causes.
The true apple blight is a malady of very serious character, that invades many orchards in the Western States. In its nature, and in the mode of its invasion, it very much resembles the dreaded fire-blight of the pear, with which most orchardists have unfortunately become already but too familiar. Like it too, all the guesses which Solons have offered for the explanation of its cause, appear equally unsatisfactory.
A whole branch or limb of the tree becomes simultaneously affected; sometimes one quarter or even one half of the top is destroyed by the disease, and the removal of the dead portions is not followed by the reproduction of healthy branches. Certain varieties are more subject to this blight than others, and they seem to poison the grafts that are inserted into them, to produce a new top to the tree with a more healthy variety.
Bitter Rot.—Our excellent and observing friend, H.N. Gillett, of Lawrence Co., Ohio, furnishes the following description of this disease to the Ohio Cultivator:
"The disease generally presents itself on the skin of the apple in very minute brown spots, from one to a dozen or more in number, generally after the fruit is pretty well grown. These gradually spread and penetrate the flesh of the apple, producing a black rot, almost as bitter as aloes, but this taste is confined to the discolored portion. The fruit ceases growing, and falls prematurely. The rot occasionally begins at the center, and extends outward, so that the fruit appears perfectly sound for some time," on which account he advises against too early gathering of the fruit.
The late Dr. Barker, of McConnellsville, Ohio, who was one of our most observing pomologists, referring to this disease as peculiar to certain varieties, concludes in an article in the paper above quoted, vide Vol. VI., p. 283, that this malady is different from what is called Bitter Rot in other places, and which affects other varieties with a discoloration of the flesh and a bitter taste. He thinks this malady is different from that described by Mr. Gillett, and that it, the true Bitter Rot, is caused by a fungous growth, the spores of which are carried on the air from tree to tree, like a similar fungus producing mold in the cherry, plum, and peach. He also traces a resemblance of this disease to the vaccination in the human subject, except that the scab does not separate and fall off. Hence he suggested the name of pock, instead of Bitter Rot. High culture, manure, lime, trimming, and pasturing hogs in the orchard, have all been recommended as remedies.
Cracked Fruit—Mildew.—Certain fruits become partially covered with what appears to be a fungous growth, which occupies the skin in such a manner as to prevent the development of the succulent tissues beneath it. This may result in a deformity consequent upon the irregular growth, and the fruit is called scabby, or it may strike deeper into the tissues, which become dry and corky and crack open, being thus utterly worthless. Some varieties, which formerly produced the most beautiful fruits, have been so severely affected by this malady as to yield absolutely nothing in certain localities, and are only rendered profitable by top grafting with other sorts that are not affected with the cracking. That this is not caused by the wearing out of the variety, as has been suggested, it may be added that the same fruit ripens perfectly and is quite fair in other regions of the country. The trouble, however, is extending, and it is hardly safe to plant largely of those varieties that have proved subject to the malady. No explanation has been satisfactory as to the cause, nor has any treatment been successful.
Dr. Kirtland addressed the Ohio Pomological Society upon this subject, and an abstract of his remarks is here given:—
"The disease known as the blight or the fire-blight, is at this day proving the most serious obstacle to the successful cultivation of the pear, in many sections of the country. Early in the present century it prevailed extensively in New England, coincidently with the spotted fever, and other disorders of a low grade of action, which at that period swept epidemically over that region of the country. It was a popular opinion that all these diseases, both of the human family and vegetable kingdom, arose from one cause;—an opinion not, however, tolerated by medical men and men of science in that day.
"Various theories have been advanced to account for the origin of this blight. Insects, frozen sap, electricity, excessive evaporation, and exhaustion of the soil, have, at different times, been assigned as the cause. Investigation of each fails to meet and explain the phenomena attendant on the rise, progress, and results of that disease. It is time they all should be abandoned, and that researches for a cause be extended in some other direction.
"As a starting point in this undertaking, I will suggest another hypothesis, which may perhaps explain the pathology of the blight, and call into use an effectual remedy or preventive. Pathology, Dr. Webster defines to be 'the doctrine of the causes and nature of diseases.'
"1. The Pear-tree blight is produced by the poisonous impression of the seeds (sporules) of a microscopic fungus.
"2. Several combinations of iron, especially the sulphate (copperas), will, to some extent, counteract that impression.
"It will be understood that these two propositions are merely hypothetical. If sustained by analogies, subsequent observations, and experience, they will be accepted as truths; if not thus sustained, they will of course be rejected.
"The extensive prevalence of the cholera, over large portions of the globe, commencing in the year 1818, led medical men to seek for its cause. Dr. Cowdell, of London, in 1848, published 'A Disquisition on Pestilential Cholera, being an attempt to explain its phenomena, nature, cause, prevention and treatment, by reference to an extrinsic fungous origin.'
"In 1849, Prof. J.K. Mitchell, of Philadelphia, issued a more elaborate work, 'On the Cryptogamous Origin of Malarious and Epidemic Fevers.' It abounds in numerous facts and correct reasoning, and should be consulted by every investigator of disease, animal and vegetable.
"These publications attracted the attention of the medical profession, both in America and Europe, so long as that epidemic continued its ravages, and the theories they advanced gained extensive credence during that time. They were, however, lost sight of when that epidemic subsided. Recently they have been substantiated as plain matters of fact, so far as malarious diseases are concerned, by the labors and investigations of Prof. J.H. Salisbury, of Cleveland.
"It is well established, then, that a number of diseases of the animal system are produced by fungi. 'Under this name botanists comprehend not only the various races of mushrooms, toadstools, and similar productions, but a large number of microscopic plants, forming the appearances called mouldiness, mildew, smut, rust, brand, dry rot, etc.' They are universally diffused in nature. It is difficult to conceive of a place where they do not exist. They are among the most numerous of all plants, in regard to genera and species, and with very few exceptions are deleterious in their impressions on the animal system. Even the palatable mushroom is always poisonous to some persons, and may become so to all under certain circumstances. It is equally evident that fungi frequently occasion diseases in the vegetable kingdom. The smut of wheat and maize, the rust of wheat, ergot of rye and grass-seeds, and specks, cracks, and discoloration of the skin of the apple and pear are of this nature.
"The microscopical examinations of Prof. Salisbury and others have detected the presence of certain species, infesting extensively pear trees about the period of attack by the blight. They have made similar discoveries that lead to the conclusion that the curl of the peach leaf, the potato disease, and the blight of pear trees, all have their origin from the cause assigned in my second proposition.
"Under this head still another disease of our fruit should be noticed. I have watched carefully the sudden and premature decay of our plum crop, at the period of its ripening, for the last fifteen years. From hints afforded by the work of Prof. Mitchell, and several microscopic observations of my own, I was induced to publish an article in 'The Florist,' of Philadelphia, in the year 1855, in which I imputed the origin of the disease to the Torula or some analagous species of parasitic fungi. The disease still prevails among us, and it is sure to destroy all the plums which escape puncture by the curculio. It is, however, generally overlooked by pomologists, and its effects are charged to the depredations of that insect. Similar disease occasionally impairs our peach and apple crops, to a less extent. Whenever it occurs on either of these varieties of fruit, the spurs and young wood blight or canker, and cease to be fruitful for several years.
"If these discoveries and analogies establish, with any degree of certainty, the hypothesis of the cryptogamous origin of the pear tree blight, we have made important progress in laying down true indications for its cure or prevention. Among the means suggested for effecting that end, certain combinations of iron have already been named. The authority for such practice is founded on the following facts:
"1. It is a popular belief that iron exerts a favorable influence over the health of fruit trees. Hence arises the practice of driving nails into the body of such trees, and loading their limbs with scraps of iron. Both the belief and the practice may be visionary, yet in such instances of popular belief, investigation usually discovers them to be founded on some shadow of truth.
"2. An intelligent and observing gentleman of Cleveland informs me that he prevents the curl of the peach leaf by depositing in the earth, about the bodies of the trees, fragments of rusty stove pipe and worthless pieces of iron.
"3. Twenty-four years since I called the attention of the public to the isolated fact, without reference to any theory, that a large pear tree in Columbiana county, Ohio, with its body surrounded with many wagon loads of boulders, scoria, scales of iron and accumulations from a blacksmith shop, retained its health, vigor, and fruitfulness, while all other pear trees in that region of country had either died, or were suffering from blight. Vide New England Farmer, December 3, 1840, page 153. At this late day this tree still continues healthy.
"4. I recollect reading in that reliable journal, Hovey's Magazine of Horticulture, some years since, a statement that the finest prize pears seen in the Parisian market, were produced by investing the growing fruits with folds of cotton or linen cloth, and daily, or oftener, moistening them with a solution of sulphate of iron. This treatment was said to result in developing the size, beauty, and quality of the fruits to a high degree, and especially to free them from parasitic blotches.
"5. Four years since, Mrs. Weller Dean, of Rockport, Ohio, informed me that blight might not only be prevented in healthy pear trees, but might be successfully arrested, in many trees, after it had made considerable progress, by means of repeatedly washing the bodies of the trees with a saturated solution of sulphate of iron (copperas), at a time when the sap is in active circulation.
"This was a confidential communication, with the condition annexed that I should thoroughly test the plan, and if it should prove successful, I was to publish it; and furthermore, if any merit or more substantial reward should be deemed due to any one by the public, she was to be the recipient.
"This plan has yet been only imperfectly tried. Age and infirmities will probably prevent its completion by me. I will therefore report that I have tested it on a number of my partially blighted pear trees, while a greater numbers has been left to die unmedicated. Of the former, not one has yet perished, while of the latter very few survive. It has appeared, in every instance, to arrest the progress of the disease, and to impart a healthy condition to the bark wherever applied. The apparent results may have been coincidences and not the effect of the remedy. There is much false experience in horticulture and agriculture, as well as in medicine.
"These views suggest the expediency of extensively applying a solution of the sulphate of iron by means of a green-house syringe or garden engine to the tops and foliage of trees, laboring under any of the diseases suspected of a cryptogamous origin. It also becomes a query whether the same agent may not be successfully employed at some period to counteract the potato disease, either by watering with it the growing plant, or washing the tubers in it in autumn, after they are dug. No injury has ever arisen to pear trees by a free use of a saturated solution of copperas.
"In conclusion, I would observe that the discovery of the cryptogamous origin of the many disorders of the human system is effecting important changes in their treatment. May we not hope that an extension of these discoveries to the vegetable kingdom, may result as favorably in shaping the practice in diseases of fruits and fruit trees?"
4th—Wounds, and the attacks of insects, may be considered more in the light of mechanical injuries by a loss of substance, hence they belong rather to the department of surgery, and can scarcely be considered as disease. The breaking of a branch, or the removal of a portion of the bark, may inflict a serious injury, but it is one which, under ordinary circumstances, will be recovered from, without any impairment of the health of the tree—unless where the wound is so large that the new growth will not soon cover it over, in which case exposure to the moisture of the atmosphere may result in decay of the woody tissues, or, if the sap exudes, at certain seasons, it may produce canker and fungous growths. In some varieties of our cultivated fruits, wounds of this character are often attended by an effusion of gummy matter; this is particularly the case with those that are known as stone-fruits, and in these the excision of a large limb is seldom followed by a deposit of woody matter in the way of healing over the wound, which is always desirable; hence in such cases particularly, it is well to cover the exposed surface with something to exclude atmospheric moisture, whether this be paint, varnish, of shellac, or common grafting wax.
Insects, by eating the foliage extensively, very materially injure the healthy condition of a tree—even the minute aphides that suck the sap from the leaves and tender bark, will seriously impair the health of our plants; but the borers that mine under the bark, extensively consuming the vital cambium, and even burrow into the solid wood, reducing it to a honeycomb, cannot fail to affect the healthy condition of the tree materially, and often cause its premature death. Some knowledge of the habits of these little creatures is considered of so great importance, that the subject will be brought before the reader's notice more at length in another part of this volume.
There is no doubt, however, that many unhealthy conditions of our trees, that might be traced to other causes, but which are not manifestly dependent upon a want of care on the part of the orchardist, nor upon a deficiency in the constitution of the soil, are often attributable to the inroads of these minute foes, which, in some cases at least, are made the scape-goats upon which is laid the blame that should be applied to our own neglect, or want of forethought and care.
After having reviewed the whole subject, it may be safe for us to conclude that what is called disease in our cultivated vegetables of whatever kind, is a departure from full health and productiveness of sound fruits. And further that this may arise from a lack of the necessary ingredients in the soil, from a want of proper conditions as to its quality and constitution, particularly with regard to the important elements of moisture, heat, and light; and especially, that this condition of unhealthiness and unproductiveness, when not an inherent failing of the variety, may in many instances be attributable to want of proper care on our part, and to our allowing the trees to injure themselves by overbearing, while we neglect to keep up the proper supply of nourishment.
In making selections of trees for planting, it is important that all weak or unhealthy varieties should be avoided. Secure healthy and vigorous stocks, that appear to be possessed of a sound constitution, even though the fruit should not be quite so fine and beautiful as that produced by some of the sickly and less vigorous varieties. There is more difference apparent, in this respect, among pears than among apples; but of the latter there are varieties that should be avoided on account of their deficient vigor. There are others that might be considered as coming under the ban, because the trees are not long-lived; and yet some of these appear to be perfectly healthy in every other respect, and seem literally to wear themselves out by excessive bearing, producing annual crops of large and handsome fruit, until, utterly exhausted, they reach a premature end.
Some varieties, that for many years yielded very fine crops of the most beautiful fruit, and of the highest character for flavor, have afterward ceased to furnish any perfect specimens—the whole crop being covered and deformed with the black scab or fungus, that prevents their development, or else ruined by the disagreeable bitter-rot which entirely spoils them for any use. Various remedies have been suggested for these maladies, all of which are more or less unsatisfactory, because from our ignorance of the causes of the troubles; these applications are wholly empirical.
The Black-knot, which has become very common in some parts of the country, is well discussed by Benjamin D. Walsh, in the Practical Entomologist, for March, 1866, page 48.
This essay is the more valuable because of the absence of the empiricism just complained of:—
"It is a black, puffy, irregular swelling on the twigs and smaller limbs of plum and cherry trees, and, in one instance that came under my personal observation of peach trees, making its first appearance in the latitude of New York early in June, and attaining its full growth by the end of July. Usually a tree, that is attacked in this manner, is affected worse and worse every year, until it is finally killed; and wherever one tree of a group is affected, the malady usually spreads to them all in process of time. In 1865 whole cherry orchards were destroyed in Western New York by this disease, and I have myself seen many groups of wild plum trees in Illinois that were gradually perishing by it; but in Southern Ohio, as I am told, the Black-knot is never met with. In the Eastern States it has been observed from time immemorial, and various contradictory opinions have been broached as to its real nature and origin.
"In 1865 I watched the Black-knot carefully through all its stages, from its earliest commencement to its complete maturity, experimenting at the same time on numerous specimens collected week after week, so as to ascertain what insects bred in it. The practical conclusion I have arrived at, is simply this:—If the diseased twigs are all cut off and destroyed early in July in the latitude of New York, or a little earlier or later according to the latitude, taking care to cut a few inches below the affected part, the Black-knot can be checked and probably entirely eradicated; but if this operation is delayed till August, it will be of no benefit whatever. Hence we can easily account for a circumstance which has puzzled many men wonderfully, viz.: That cutting off and burning the diseased twigs is pronounced by some to be a sovereign remedy, and by others to be a delusive humbug. Those that do this early enough, find it effectual; those that delay it till too late, find it of no use.
"This perhaps will be sufficient for some few impatient souls, who take everything upon trust that they see in print, and care nothing about the rationale of a mode of treatment, so long as it be practically available. But for the benefit of that large class of intelligent agriculturists, who have been deluded by too many quack prescriptions to place much faith in any man's ipse dixit, and who in any case like to understand the principle of a remedy before they apply it, I subjoin a full account of all that is at present known on this subject, and of the different theories respecting it entertained by different writers.
"Three radically different theories have been broached as to the nature and origin of Black-knot: 1st, that it is a mere disease of the tree, like the cancer or the gout in the human race, which is the view maintained by Dr. Fitch, the State Entomologist of New York; 2d, that it is what naturalists term a "gall," produced by some unknown insect depositing its eggs in the twig—just as the well-known "oak-apples" are produced by a Gall-fly, (Cynips), depositing its egg in the bud of the oak—which is the opinion that I myself formerly held and maintained, before I had fully examined into the subject; (Proceedings Ent. Soc., Phil., III, p.p. 613-618;) and 3d, that it is what botanists term an epiphytous fungus, growing on the tree as a mushroom or toad-stool grows on the ground, which is the opinion of the botanist Schweinitz, and which has recently been re-asserted by Mr. Glover, the Entomologist of the Bureau of Agriculture at Washington, (Ag'l Rep., 1863, p. 572.) This last is the opinion which, upon full inquiry, I have now adopted.
"Before discussing these theories, the facts arrived at by myself in the summer of 1865, must first be briefly noticed. It should be premised that the old, dry Black-knot remains on the tree for many years, and that the place to look for the new Black-knot is on such trees as have been already attacked and are loaded with old Black-knot, without being as yet completely killed by it.
"1st. By the middle of June the new Black-knot is pretty well developed, and may then be readily distinguished from the old by its dull, opaque, brown-black color, while the old is coal-black and more or less glossy. When cut into, it is found to be fleshy inside, like an apple, but not juicy, and of a pale greenish-yellow color, with fibres radiating from the axis of the twig, while the old Black-knot is internally hard and woody, and of a reddish-brown or rust-red color. The brown-black color of the external surface is retained till the last week in July, when the surface of the new Black-knot becomes gradually covered all over with little, coal-black, hemispherical plates, appearing when viewed through a pocket glass, about the size of the head of a pin, each of these is a distinct fungus, named long ago by Schweinitz 'Sphæria morbosa.' Even on the old Black-knot this fungus may be readily seen, at any time of the year, covering its entire surface. So far I have added little to the information already published on this subject, except by the specification of dates. But in addition to these facts, I discovered that about the last of July or the first week in August, there grows from each fungus on the surface of the Black-knot a little cylindrical filament about one-eighth of an inch long, which no doubt bears the seed or "spores," as they are technically termed, of the fungus, and that these filaments very shortly afterwards fall off and disappear, leaving behind them the hemispherical plates, which alone had been hitherto noticed by the botanists. In another Epiphytous fungus, which grows commonly and abundantly in Illinois on the Red Cedar, but which differs from the Black-knot in being attached to the twig by a very short stalk or peduncle, and in being roundish and externally of a reddish-brown color instead of elongate and black, there is a precisely similar phenomenon; except that the plates and filaments are very much larger, and that each filament, when it falls off, leaves a ragged scar behind it. In a single specimen of Black-knot noticed August 6th, I discovered that the filaments not only covered the entire surface of the Black-knot itself, except where a few of them had already fallen off, but that they were thinly studded over the twig for an inch or two above and below the swollen black part; thus proving that the fungus sometimes extends rather further than on a cursory view it would appear to do. Towards the middle of August, the new Black-knot, having perfected its seed, gradually dries up and becomes internally of a reddish-brown color. In other words, like so many other annual plants, it dies shortly after it has perfected its seed, just as a stalk of wheat or of corn dies shortly after the grain is ripe.
"2d. During the months of June and July I collected from time to time very numerous specimens of Black-knot, some of which I cut into to see what larvæ they contained, and some I preserved to see what perfect insects could be bred from them. Besides seven specimens of the common "Curculio," which many persons had previously bred from Black-knot, I bred for the first time therefrom no less than five distinct species of insects, none of which can be considered as gall-makers, but not a single true gall-maker; and I can confirm Dr. Fitch's assertion, that some specimens are wholly free from larvæ of any kind when cut into.
"We will now take up in order the three different theories respecting the nature and origin of Black-knot, which, as already stated, have been maintained by different writers.
"1st. That Black-knot is a mere disease like the cancer.—Dr. Fitch, who maintains this opinion, allows that the black granules found on the Black-knot are a true fungus, 'that the surface of these excrescences, when mature, is always covered with this plant,' and that 'this plant never grows, or at least has never been found, in any other situation.' (Address N.Y. State Ag'l Soc., 1860, p. 21.) * * *
"2d. That Black-knot is a gall.—As already stated, there is no true gall-making insect that inhabits the Black-knot, so far as I can discover on the fullest and most extensive investigation that I have been able to give to the subject. The minute holes commonly found in the old dry Black-knot, which are too large either for the 'Curculio' or for the small moths bred by myself from Black-knot, are of a suitable size for either of the two dipterous' insects which I have enumerated in a note as bred by myself from Black-knot. Consequently the argument which I based upon the existence of these minute holes (Proc. Ent. Soc. Phil. III, p. 614) falls to the ground; and although I found on one occasion the larva of a Gall-gnat embedded in a cell in a Black-knot, yet this was most probably that of the Guest Gall-gnat which I actually bred from Black-knot, as stated in the note, and not of a true gall-making Gall-gnat.
"3d. That Black knot is a fungus.—Just as Dr. Fitch, having proved to his own satisfaction that Black-knot is neither a gall nor a fungus, infers by the method of exhaustion that it must be a disease; so, having proved that it is neither a disease nor a gall, we may infer by the method of exhaustion that it must be a fungus, or rather an assemblage of funguses. In confirmation of this theory may be adduced the very remarkable analogies between the structure of the Black-knot and that of the fungus, described above as occurring on Red Cedar. That this last is really and truly a fungus and not a gall, is shown by the fact, that it is scarcely ever inhabited by insects; for out of hundreds of specimens that I have cut into, both green and dry, not more than two or three contained the larvæ of the moths, but one contained what was probably the larva of an Ichneumon-fly, and all the rest were perfectly solid and unbored. On the other hand, Black-knot is so infested by insects, that it is almost impossible to find a mature specimen that is not all bored up by them. The cause of this remarkable difference may be attributed to the well-known repugnance of almost all kinds of insects for Red Cedar.
"If, then, Black-knot is a fungus, and if, as I think I have shown, it is an annual plant propagating itself by seed or the so-called 'spores,' and the 'spores' make their appearance about the end of July in latitude 41° 30', then it must be obvious that if all the Black-knot on a particular tree is cut off and destroyed in the fore-part of July, or a little earlier or later as you go further south or further north, an effectual stop will be put to its further propagation. It is true that the 'spores' are in the form of an impalpable powder, so that they may be carried some considerable distance from other infected trees by the wind; and it may possibly be further true, that certain 'spores' may lie dormant in the bark for over a year, as the seeds of weeds will often lie dormant in the ground. Still, with all these possible drawbacks, I have little doubt that the above remedy will, as a general rule, if applied according to directions, be found effectual."
The foregoing is interesting as giving the conclusions of an entomologist who had investigated the subject, and arrived at the same result that had been reached by a botanist many years before. Schweinitz, in 1832, published the correct history of the Black-knot in the Transactions of the American Philosophical Society. In the American Agriculturist, April, 1863, p. 113, Mr. C.F. Austin confirmed Schweinitz's observations, and gave a popular account of the botany of this fungus, with figures. It may be considered as fully established that the knot is of vegetable origin; and whenever insects or larvæ are found in it, it is only because they find a diseased portion of the tree suited to their necessities.
Rot and Mildew upon the grape both destroy our crops, and render the vines unhealthy. Would that I were able to give the reader some encouragement as to its cause and prevention, or cure; but some of our oldest and most experienced vine-planters have come to the conclusion, as to treatment, that "the more they find out, the more they don't know." It is now generally conceded that it is caused by a fungus growth. That on the leaves is probably the Oidium Tuckeri, and it is generally supposed that the mildew and rot of the berries is owing to the same cause. The microscope clearly indicates its fungoid character. As to the causes, it must be admitted that the weather favors or prevents its access, and that so far it is a proximate cause, but that the spores are the true origin of the trouble. The Cincinnati Horticultural Society, whose members have long had opportunities of studying this malady, have come to the following conclusions, which, it will be seen, are not very satisfactory.
To the Cincinnati Horticultural Society:—We have been appointed by you to discharge a certain function. Having examined the premises and considered the subject, we do now report: That, notwithstanding the discouragements attendant upon the experience of most vine-dressers during the past season, we are determined to persevere in viticulture, for the following among other reasons:
We have our capital invested in a way which has been profitable, and we believe will be so again.
Our lands are occupied with a growth that has required time and labor to produce, and which we are unwilling to sacrifice.
We do not believe that the diseases to which the vines and fruit have been subjected, are dependent upon long pruning or short pruning, upon deep culture or shallow, nor any of the causes to which it has been attributed, that are under the immediate control of man, but that the cause is CLIMATIC.
We do not believe that the rot and mildew can be warded off by leaving the wood upon the vines, nor that the usual vineyard method called short pruning, will render our vineyards more subject to this disease.
We do believe, however, that we have yet much to learn in regard to the philosophy of pruning which it were well for us to study, and that by so doing we may gather some useful hints in relation to this very important part of a vine-grower's duties.
We do believe, as a result of our observations, that some varieties of grapes are more healthy and vigorous than others; and, on the other hand, that some are peculiarly subject to the inroads of these maladies which have so terribly affected the fruit, the foliage, and the green wood of our vines. We do firmly believe, that our societies should avoid recommending the extensive planting of any trees or vines that have not proved themselves general healthy, and free from the maladies in question, for a number of years, after trial in different situations.
We do believe that systematic efforts should be made with different remedial and preventive agents, to avert the disasters that have overtaken our vine-crops of late years, and, with this view, as we have reason to believe that the difficulty depends upon the existence of some epiphytic plant, and as we are informed that sulphur and sulphate of iron exert an obnoxious influence upon the whole class of fungi, we recommend our brother vine-dressers to take courage, and to make vigorous and systematic efforts to ward off the difficulty the coming season, by the regular and persevering applications of these substances to their grape vines.
For your encouragement, we will also refer you to the history of the vineyards of Europe, which have suffered in like manner, and which have at length recuperated their energies and become productive. Why may not the same good fortune await us?
Very respectfully submitted, by
R. Buchanan, Chairman.