CULTIVATION.
Y noting the conditions in which plants are found growing in a natural state, we obtain some clue to their successful management, when placed under conditions more or less artificial; and, in the case of Cactuses, knowledge of this kind is of more than ordinary importance. In the knowledge that, with only one or two exceptions, they will not exist in any but sunny lands, where, during the greater part of the year, dry weather prevails, we perceive what conditions are likely to suit them when under cultivation in our plant-houses.
Cactuses are all American (using this term for the whole of the New World) with only one or two exceptions (several species of Rhipsalis have been found wild in Africa, Madagascar, and Ceylon), and, broadly speaking, they are mostly tropical plants, not-withstanding the fact of their extending to the snow-line on some of the Andean Mountains of Chili, where several species of the Hedgehog Cactus were found by Humboldt on the summit of rocks whose bases were planted in snow. In California, in Mexico and Texas, in the provinces of Central and South America, as far south as Chili, and in many of the islands contiguous to the mainland, the Cactus family has become established wherever warmth and drought, such as its members delight in, allowed them to get established. In many of the coast lands, they occur in very large numbers, forming forests of strange aspect, and giving to the landscape a weird, picturesque appearance. Humboldt, in his "Views of Nature," says: "There is hardly any physiognomical character of exotic vegetation that produces a more singular and ineffaceable impression on the mind of the traveller than an arid plain, densely covered with columnar or candelabra-like stems of Cactuses, similar to those near Cumana, New Barcelona, Cora. and in the province of Jaen de Bracamoros." This applies also to some of the small islands of the West Indies, the hills or mountains of which are crowned with these curious-looking plants, whose singular shapes are alone sufficient to remind the traveller that he has reached an American coast; for these Cactuses are as peculiar a feature of the New World as the Heaths are in the Old, or as Eucalypti are in Australia.
Although the Cactus order is, in its distribution by Nature, limited to the regions of America, yet it is now represented in various parts of the Old World by plants which are apparently as wild and as much at home as when in their native countries.
The Indian Figs are, perhaps, the most widely distributed of Cactuses in the Old World—a circumstance due to their having been introduced for the sake of their edible fruits, and more especially for the cultivation of the cochineal insect. In various places along the shores of the Mediterranean, and in South Africa, and even in Australia, the Opuntias have become naturalised, and appear like aboriginal inhabitants. It is, however, only in warm sunny regions that the naturalisation of these plants is possible.
From these facts, we are able to form some general idea of the conditions suitable for Cactuses when cultivated in our greenhouses; for, although we seldom have, or care to have, any but diminutive specimens of many of these plants as compared with their appearance when wild, yet we know that the same conditions as regards heat, light, and moisture are necessary for small Cactuses as for full-grown ones.
Although the places in which Cactuses naturally abound are, for the greater portion of the year, very dry and warm, heavy rains are more or less frequent during certain periods, and these, often accompanied by extreme warmth and bright sunshine, have an invigorating and almost forcing effect on the growth of Cactuses. It is during this rainy period that the whole of the growth is made, and new life is, as it were, given to the plant, its reservoir-like structure enabling it to store up a large amount of food and moisture, so that on the return of dry weather the safety of the plant is insured.
It is to the management of Cactuses in a small state, such as is most convenient for our plant-houses, and not to the cultivation of those colossal species referred to above, that the instructions given here will be for the most part devoted; but, as in the case of almost every one of our cultivated plants, it is important to the cultivator to know something of the conditions which Nature has provided for Cactuses in those lands where they are native.
There is nothing in the nature or the requirements of Cactuses that should render their successful management beyond the means of anyone who possesses a small, heated greenhouse, or even a window recess to which sunlight can be admitted during some portion of the day. In large establishments, such as Kew, it is possible to provide a spacious house specially for the cultivation of an extensive collection, where many of them may attain a good size before becoming too big. And it will be evident that where a house such as that at Kew can be afforded, much more satisfactory results may generally be obtained, than if plants have to be provided for in a house containing various other plants, or in the window of a dwelling-room. Apart altogether from size, it is, however, possible to grow a collection of Cactuses, and to grow them well, in a house of small dimensions—given the amount of sunlight and heat which are required by these plants. We sometimes see Cactuses—specimens, too, of choice and rare kinds—which have been reared in a cottager's window or in a small greenhouse, and which in health and beauty have at least equalled what has been accomplished in the most elaborately prepared houses. It may be said that these successes, under conditions of the most limited kind, are accidental rather than the result of properly understood treatment; but however they have been brought about, these instances of good cultivation are sufficient to show that success is possible, even where the means are of the simplest or most restricted kind. Whether it be in a large house, fitted with the best arrangements, or in the window of the cottager, the conditions essential to the successful cultivation of Cactuses are practically the same.
In Wardian Cases.—Many of our readers will be acquainted with the neat little glass cases, like greenhouses in shape, and fitted up in much the same way, which are sometimes to be seen in our markets, filled with a collection of miniature Cactuses. To the professional gardener, these cases are playthings, and are looked upon by him as bearing about the same relation to gardening as a child's doll's house does to housekeeping. Not-withstanding this, they are the source of much interest, and even of instruction, to many of the millions to whom a greenhouse or serious gardening is an impossibility. In these little cases—for which we are indebted to Mr. Boller, a dealer in Cactaceous plants—it is possible to grow a collection of tiny Cactuses for years, if only the operations of watering, potting, ventilating, and other matters connected with ordinary plant growing, are properly attended to.
In Window Recesses.—In the window recess larger specimens may be grown, and here it is possible to grow and flower successfully many of the plants of the Cactus family. In a window with a south aspect, and which lights a room where fires are kept, at least during cold weather, specimens of Phyllocactus, Cereus flagelliformis, Epiphyllum, and, in fact, of almost every kind of Cactus, are sometimes to be met with even in England; whilst in Germany they are as popular among the poorer classes as the Fuchsia, the Pelargonium, and the Musk are with us. One of the commonest of Cactuses in the latter country is the Rat's-tail Cactus (Cereus flagelliformis), and it is no unusual thing to see a large window of a cottager's dwelling thickly draped on the inside with the long, tail-like growths and handsome rose-coloured flowers of this plant. This is only one among dozens of species, all equally useful for window gardening, and all as interesting and beautiful as those above described.
In Greenhouses.—For the greenhouse proper, Cactuses are well adapted, either as the sole occupants or as suitable for such positions as are afforded by shelves or baskets placed near the roof glass. If the greenhouse is not fitted with heating arrangements, then, by selecting only those species of Cactus that are known to thrive in a position where, during winter, they are kept safe out of the reach of frost (of which a large number are known) a good collection of these plants may be grown. In heated structures the selection of kinds may be made according to the space available, and to the conditions under which they will be expected to grow. Fig. 3 represents a section of a house for Cactuses, which will afford a good idea of the kind of structure best suited for them. The aspect is due south.
FIG. 3.—SECTION OF HOUSE FOR CACTUSES—A,A, Hot-water Pipes; B,B, Ventilators
When grown on their own roots, the Epiphyllums, as well as the pendent-growing kinds of Rhipsalis, and several species of Cereus, may be placed in baskets and suspended from the roof. The baskets should be lined with thin slices of fibrous peat, and the whole of the middle filled with the compost recommended for these plants under "Soil". When well managed, some very pretty objects are formed by the Epiphyllums grown as basket plants. The climbing Cactuses are usually planted in a little mound composed of loam and brick rubble, and their stems either trained along rafters or allowed to run up the back wall of a greenhouse, against which they root freely, and are generally capable of taking care of themselves with very little attention from the gardener.
In Frames.—For cultivation in frames, the conditions are the same as for greenhouses. Even when grown in the latter, it will be found conducive to the health and flowering of the plants if, during the summer months, they can be placed in a frame with a south aspect, removing them back to the house again on the decline of summer weather. Wherever the place selected for Cactuses may be, whether in a large plant-house, or a frame, or a window, it is of vital importance to the plants that the position should be exposed to bright sunshine during most of the day. Without sunlight, they can no more thrive than a Pelargonium could without water. In Germany, many growers of almost all the kinds of Cactuses place their young plants in frames, which are prepared as follows: In April or May a hot-bed of manure and leaves is prepared, and a frame placed upon it, looking south. Six inches of soil is put on the top of the bed, and in this, as soon as the temperature of the bed has fallen to about 70 deg., the young plants are placed in rows. The frames are kept close even in bright weather, except when there is too much moisture inside, and the plants are syringed twice daily in dry, hot weather. The growth they make under this treatment is astonishing. By the autumn the plants are ready to be ripened by exposure to sun and air, and in September they are lifted, planted in pots, and sent to market for sale. This method may be adopted in England, and if carefully managed, the growth the plants would make would far exceed anything ever accomplished when they are kept permanently in pots.
Out-of-doors.—There are some kinds which may be grown out of doors altogether, if planted on a sunny, sheltered position, on a rockery. The most successful plan is that followed at Kew, where a collection of the hardier species is planted in a rockery composed of brick rubble and stones. During summer the plants are exposed; but when cold weather and rains come, lights are placed permanently over the rockery, and in this way it is kept comparatively dry. No fire-heat or protection of any other kind is used, and the vigorous growth, robust health, and floriferousness of the several species are proofs of the fitness of the treatment for this class of plants.
In any garden where a few square yards in a sunny, well-drained position can be afforded for a raised rockery, the hardy Cactuses may be easily managed. To make a suitable rockery, proceed as follows: Find a position against the south wall of a house, greenhouse, or shed, and against this wall construct a raised rockery of brick rubble, lime rubbish, stones (soft sandstone, if possible), and fibrous loam. The rockery when finished should be, say, 4 ft. wide, and reach along the wall as far as required; the back of the rockery would extend about 2 ft. above the ground level, and fall towards the front. Fix in the wall, 1 ft. or so above the rockery, a number of hooks at intervals all along, to hold in position lights sufficiently long to cover the rockery from the wall to the front, where they could be supported by short posts driven in the ground. The lights should be removed during summer to some shed, and brought out for use on the approach of winter. Treated in this manner, the following hardy species could not fail to be a success:
Opuntia Rafinesquii
and var.
arkansana, O. vulgaris, O. brachyarthra, O. Picolominiana, O. missouriensis, O. humilis, Cereus Fendleri, C. Engelmanni, C. gonacanthus, C. phoeniceus, Echinocactus Simpsoni, E. Pentlandii, Mamillaria vivipara.
Having briefly pointed out the various positions in which Cactuses may be cultivated successfully, we will now proceed to treat in detail the various operations which are considered as being of more or less importance in their management. These are potting, watering, and temperatures, after which propagation by means of seeds, cuttings, and grafting, hybridisation, seed saving, &c., and diseases and noxious insects will be treated upon.
Soil.—The conditions in which plants grow naturally, are what we usually try to imitate for their cultivation artificially. At all events, such is supposed to be theoretically right, however difficult we may often find it to be in practice. Soil in some form or other is necessary to the healthy existence of all plants; and we know that the nature of the soil varies with that of the plants growing in it, or, in other words, certain soils are necessary to certain plants, whether in a state of nature or cultivated in gardens. But, whilst admitting that Nature, when intelligently followed, would not lead us far astray, we must be careful not to follow her too strictly when dealing with the management of plants in gardens. There are other circumstances besides the nature of the soil by which plants are influenced. Soil is only one of the conditions on which plants depend, and where the other conditions are not exactly the same in our gardens as in nature, it is often found necessary to employ a different soil from that in which the plants grow when wild.
It has been stated that plants do not grow naturally in the soil best suited for them, and that the reason why many plants are found in peculiar places is not at all because they prefer them, but because they alone are capable of existing there, or because they take refuge there from the inroads of stouter neighbours who would destroy them or crowd them out. There are, as every gardener knows, numerous plants that succeed equally well in widely different soils, and a soil which may be suitable for a plant in one place, may prove totally unsuited in another. Hence it is why we find one gardener recommending one kind of soil, and another a different one, for the same plant, both answering equally well because of other conditions fitting better with each soil. This helps us to understand how it is that many garden subjects grow much better when planted in composts often quite different from those the plants are found in when wild. Few plants have a particular predilection for soil, and some have what we may call the power to adapt themselves to conditions often widely different.
In Cactuses we have a family of plants for which special conditions are necessary; and, as regards soil, whether we are guided by nature or by gardening experience, we are led to conclude that almost all of them thrive only when planted in one kind, that soil being principally loam. Plants which are limited in nature to sandy, sun-scorched plains or the glaring sides of rocky hills and mountains, where scarcely any other form of vegetation can exist, are not likely to require much decayed vegetable humus, but must obtain their food from inorganic substances, such as loam, sand, or lime. So it is with them when grown in our houses. They are healthiest and longest-lived when planted in a loamy soil; and although they may be grown fairly well for a time when placed in a compost of loam and leaf mould, or loam and peat, yet the growth they make is generally too sappy and weak; it is simply fat without bone, which, when the necessary resting period comes round, either rots or gradually dries up. In preparing soil, therefore, for all Cactuses (except Epiphyllum and Rhipsalis, which will be treated separately) a good, rather stiff loam, with plenty of grass fibre in it, should form the principal ingredient, sand and, if obtainable, small brick rubble being added—one part of each of the latter to six parts of the former. The brick rubble should be pounded up so that the largest pieces are about the size of hazel nuts. Lime rubbish, i.e., old plaster from buildings, &c., is sometimes recommended for Cactuses, but it does not appear to be of any use except as drainage. At Kew its use has been discontinued, and it is now generally condemned by all good cultivators. Of course, the idea that lime was beneficial to Cactuses sprang from the knowledge that it existed in large quantities in the soil in which the plants grew naturally, and it is often found in abundance, in the form of oxalate of lime, in the old stems of the plants. But in good loam, lime, in the state of chalk, is always present, and this, together with the lime contained in the brick rubble, is sufficient to supply the plants with as much as they require.
For Epiphyllums and Rhipsalis, both of which are epiphytal naturally, but which are found to thrive best in pots in our houses, a mixture of equal parts of peat and loam with sand and brick rubble in the same proportion as before recommended, will be found most suitable. Leaf mould is sometimes used for these plants; but unless really good it is best left out of the soil. The finest Epiphyllums have been grown in a soil which consists almost wholly of a light fibry loam, with the addition of a little crushed bones.
Potting.—Cactuses, when healthy, are injuriously affected by frequent disturbance at the roots. On the arrival of the potting season, which for these plants is in April and May, established plants should be examined at the root, and if the roots are found to be in a healthy condition, and the soil sweet, they should be replaced in the same pots to continue in them another year. If the roots are decayed, or the soil has become sour, it should be shaken away from the roots, which must be examined, cutting away all decayed portions, and shortening the longest roots to within a few inches of the base of the plant. Cactuses are so tenacious of life, and appear to rely so little on their roots, that it will be found the wisest plan, when repotting them, to cut the roots thoroughly.
The size of pots most suitable is what would be considered small in comparison with other plants, Cactuses preferring to be somewhat cramped in this respect. This, indeed, is how they are found when wild, the roots generally fixing themselves in the crevices of the rocks or stones about which the plants grow, so that a large specimen is often found to have only a few inches of space in the cleft of a rock for the whole of its roots. When thus limited, growth is firmer and the flowers are produced in much greater profusion than when a liberal amount of root space is afforded. The pots should be well drained-about one-fifth of their depth filled with drainage when intended for large, strong-growing kinds, and one-third for the smaller ones, such as Mamillarias. A layer of rough fibry material should be placed over the crocks to prevent the finer soil from stopping the drainage. When filling in the soil, press it down firmly, spreading the roots well amongst it, and keeping the base of the plant only an inch or so below the surface.
For plants with weak stems, stakes will be necessary, and even stout-stemmed kinds, when their roots are not sufficient to hold them firmly, will do best if fastened to one or two strong stakes till they have made new roots and got firm hold of the soil. Epiphyllums, when grown as standards, should be tied to strong wire supports, those with three short, prong-like legs being most desirable, as, owing to the weight of the head of the plant, a single stake is not sufficient to hold the whole firmly. After potting, no water should be given for a few weeks. In fact, if the atmosphere in which the plants are placed be kept a little moist, it will not be necessary to water them till signs of fresh growth are perceived. For Epiphyllums and Rhipsalis, water will be required earlier than this; but even they are best left for a few days without water, after they have been repotted. As soon as fresh growth is perceived, the plants may be well watered, and from this time water may be supplied as often as the soil approaches dryness. Newly-imported plants, which on arrival are usually much shrivelled and rootless, should be potted in rather dry soil and small pots, and treated as recommended above. Cactuses, we must remember, contain an abundance of nourishment stored up in their stems, and upon this they will continue to exist for a considerable time without suffering; and, when their growing season comes round, root action commences whether the soil is wet or dry, the latter being the most favourable.
Plants altogether exposed to the air will push roots in due time. A remarkable instance of this has been recorded by Mr. J. R. Jackson, curator of the museums at Kew. A plant of Pilocereus senilis, which had grown too tall for the house, was cut off at the base, and placed in the museum as a specimen. Here it gradually dried up to within 2 ft. of the top, where a fracture across the stem had been made. Above this the stem remained fresh and healthy, and, on examining it some months afterwards, it was found that not only had the top of the stem remained green, but it had formed roots of its own, which had grown down the dead lower portion of the stem, and were in a perfectly healthy state. When it is remembered that all this happened in the dry atmosphere of a museum, it will be apparent how exceptional Cactuses are in their manner of growth, and in the wonderful tenacity of life they exhibit under conditions which would destroy the majority of plants in a very short time. We sometimes find, when examining the bases of Cactus stems, that decay has commenced; this is carefully cut out with a sharp knife, and the wound exposed to the action of the air till it is perfectly dry, or, as we term it, "callused."
Watering.—It will have peen gathered from what has been previously said in relation to the conditions under which the majority of the plants of the Cactus family grow when wild, that during their season of growth they require a good supply of moisture, both at the root and overhead; and afterwards a somewhat lengthened period of rest, that is, almost total dryness, accompanied by all the sunlight possible, and generally a somewhat high temperature. The growing season for all those kinds which require to be kept dry when at rest is from the end of April to the middle of August, and during this time they should be kept moderately moist, but not constantly saturated, which, however, is not likely to occur if the water is not carelessly supplied, and the drainage and soil are perfect. This treatment corresponds with what happens to Cactuses in a wild state, the frequent and heavy rains which occur in the earlier part of the summer in the American plains supplying the amount of moisture necessary to enable these plants to make fresh growth, and produce their beautiful flowers and spine-clothed fruits. After August, little or no rain falls, and the Cactuses assume a rather shrivelled appearance, which gives them an unhealthy look, but which is really a sign of ripeness, promising a plentiful crop of flowers when the rainy season again returns.
As the sun in England is not nearly so powerful as in the hot plains of Central America and the Southern States of North America, where Cactuses are found in greatest abundance, it will be evident that, if flowers are to be produced, we must see that our plants have a sufficiency of water in early summer, and little or none during the autumn and winter, whilst the whole year round they should be exposed to all the sunlight possible, the temperature, of course, varying with the requirements of the species, whether it is a native of tropical or of temperate regions. It is important that the cultivator should understand that if water is liberally supplied all through the summer, the plants cannot obtain the rest which is necessary to their ripening and producing flowers, as dryness at the root alone is not sufficient to provide this, but must be accompanied by exposure to bright sunlight, which is not possible in England during winter, so that the ripening process must begin before the summer is over.
It is possible to preserve most Cactuses alive by keeping them constantly growing; but, with very few exceptions, such treatment prevents the plants from flowering. The following is what is practised in the gardens where Cactuses are successfully cultivated. For the genera Cereus, Echinopsis, Echinocactus, Mamillaria, Opuntia, and Melocactus, a moist tropical house is provided, and in April the plants are freely watered at the root, and syringed overhead both morning and afternoon on all bright days. This treatment is continued till the end of July, when syringing is suspended, and the water supplied to the roots gradually reduced. By the end of August, the plants are placed in a large light frame with a south aspect, except the tall-growing kinds, which are too bulky to remove. In this frame the plants are kept till the summer is over, and are watered only about once a week should the sun be very powerful. The lights are removed on all bright sunny days, but are kept on during wet or dull weather, and at night. Under this treatment, many of the species assume a reddish appearance, and the thick fleshy-stemmed kinds generally shrivel somewhat. There is no occasion for alarm in the coloured and shrivelled appearance of the plants: on the contrary, it may be hailed as a good sign for flowers.
A common complaint in relation to Cacti as flowering plants is that they grow all right but rarely or never flower. The explanation of this is shown by the fact that the plants must be properly ripened and rested before they can produce flowers. On the approach of cold weather the plants which were removed to a frame to be ripened should be brought back into the house for the winter, and kept quite dry at the roots till the return of spring, when their flowers will be developed either before or soon after the watering season again commences.
Hitherto we have been dealing with those genera which have thick fleshy stems; but there still remain the genera Rhipsalis, Epiphyllum, and Phyllocactus, which are not capable of bearing the long period of drought advised for the former. The last-mentioned genus should, however, be kept almost dry at the root during winter, and, if placed in a light, airy house till the turn of the year, the branches will ripen, and set their flower buds much more readily than when they are wintered in a moist, partially-shaded house. During summer all the Phyllocactuses delight in plenty of water, and, when growing freely, a weak solution of manure affords them good food. Epiphyllums must be kept always more or less moist at the root, though, of course, when growing freely, they require more water than when growth has ceased for the year, which happens late in autumn. The same rule applies to Rhipsalis, none of the species of which are happy when kept long dry. For the several species of Opuntia and Echinopsis, which are sufficiently hardy to be cultivated on a sunny rockery out of doors, it will be found a wise precaution to place either a pane of glass or a handlight over the plants in wet autumns and during winter, not so much to serve as protection from cold as to shield them from an excess of moisture at a time when it would prove injurious.
Temperature.—As the amount of heat required by the different species of Cactus varies very considerably, and as the difference between the summer and winter temperatures for them is often as great as it is important, it will be as well if we mention the temperature required by each when describing the species. It is true that the majority of Cactuses may be kept alive in one house where all would be subjected to the same temperature, but many of the plants would merely exist, and could not possibly flower. It would be easy to point to several instances of this unsatisfactory state of things. At Kew, for example, owing to the arrangements necessary for the public, it is found convenient to have the majority of the large collection of Cactuses in one house, where the plants present an imposing appearance, but where, as might be expected, a good number of the species very rarely produce flowers. The Cactuses which inhabit the plains of the Southern United States are subjected to a very high summer temperature, and a winter of intense cold; whilst on the other hand the species found in Central and South America do not undergo nearly so wide an extreme, the difference between the summer and winter temperatures of these countries being generally much less marked. A word will be said under each species as to whether it is tropical, temperate, or hardy, a tropical temperature for Cacti being in summer 70 degs., rising to 90 degs. with sun heat, night temperature 60 degs. to 70 degs., in winter 60 degs. to 65 degs. Temperate: in summer 60 degs., rising to 75 degs. with sun heat, night 60 degs. to 65 degs., in winter 50 degs. to 55 degs. The hardy species will, of course, bear the ordinary temperatures of this country; but, to enable them to withstand a very cold winter, they must be kept as dry as possible. In the colder parts of England it is not advisable to leave any of these plants outside during winter.
Insect Pests.—Notwithstanding the thickness of skin characteristic of almost every one of the Cactuses, they are frequently attacked by various kinds of garden pests when under cultivation, and more especially by mealy bug. There is, of course, no difficulty in removing such insects from the species with few or no spines upon their stems; but when the plants are thickly covered with clusters of spines and hairs, the insects are not easily got rid of. For Cactuses, as well as for other plants subject to this most troublesome insect, various kinds of insecticide have been recommended; but the best, cheapest, and most effectual with which we are acquainted is paraffin, its only drawback being the injury it does to the plants when applied carelessly, or when not sufficiently diluted. A wineglassful of the oil, added to a gallon of soft water, and about 2oz. of soft soap, the whole to be kept thoroughly mixed by frequently stirring it, forms a solution strong enough to destroy mealy bug. In applying this mixture, a syringe should be used, or, if the plants are to be dipped overhead, care must be taken to have the oil thoroughly diffused through the water, or the plant, when lifted out, will be covered with pure paraffin, which does not mix properly with water, but swims upon the surface if allowed to stand for a few moments. The plants should be laid on their sides to be syringed with the mixture, and after they have been thoroughly wetted, they may be allowed to stand for a few minutes before being syringed with pure water. Plants that are badly infested with mealy bug should be syringed with the paraffin mixture once a day, for about a week. It is easy to do serious harm to these plants by using a stronger solution than is here recommended, and also by not properly mixing the oil with the soap and water; and the amateur cannot, therefore, be too careful in his use of this excellent insecticide. It would be easy to recommend other insecticides, so called, for Cactuses; but whilst they are less dangerous to the plants, they are often as harmless as pure water to the insects.
For scale, which sometimes infests these plants, and which is sometimes found upon them when wild, the paraffin may be used with good effect.
Thrips attack Phyllocactus, Rhipsalis, and Epiphyllum, especially when the plants are grown in less shade, or in a higher temperature, than is good for them. Fumigation with tobacco, dipping in a strong solution of tobacco, or sponging with a mixture of soap and water, are either of them effectual when applied to plants infested with thrips. The same may be said of green-fly, which sometimes attacks the Epiphyllums.
A blight, something similar to mealy bug, now and again appears on the roots of some of the varieties of Echinocactus and Cereus. This may be destroyed by dipping the whole of the roots in the mixture recommended for the stems when infested by mealy bug, and afterwards allowing them to stand for a few minutes immersed in pure water. They may then be placed where they will dry quickly, and finally, in a day or two, repotted into new compost, first removing every particle of the old soil from the roots.
Diseases.—When wild and favourably situated as regards heat and moisture, the larger kinds of Cactus are said to live to a great age, some of the tree kinds, according to Humboldt, bearing about them signs of having existed several hundred years. The same remarkable longevity, most likely, is found in the smaller kinds when wild. Under artificial cultivation there are, however, many conditions more or less unfavourable to the health of plants, and, in the case of Cactuses, very large specimens, when imported from their native haunts to be placed in our glass houses, soon perish. At Kew, there have been, at various times, very fine specimens of some of the largest-growing ones, but they have never lived longer than a year or so, always gradually shrinking in size till, finally, owing to the absence of proper nourishment, and to other untoward conditions, they have broken down and rotted. This rotting of the tissue, or flesh, of these plants is the great enemy to their cultivation in England. When it appears, it should be carefully cut out with a sharp knife, and exposed to the influence of a perfectly dry atmosphere for a few days till the wound has dried, when the plant should be potted in a sandy compost and treated as for cuttings. Sometimes the decay begins in the side of the stem of the plant, in which case it should be cut away, and the wound exposed to a dry air. The cause of this decay at the base or in the side of the stems of Cactuses is no doubt debility, which is the result of the absence of some necessary condition when the plants are cultivated in houses or windows in this country.
Grafted plants, especially Epiphyllums, when worked on to Pereskia stocks, are apt to grow weak and flabby through the stem wearing out, or through the presence of mealy bug or insects in the crevices of the part where the stock and scion join, in which case it is best to prepare fresh stocks of Pereskia, and graft on to them the best of the pieces of Epiphyllum from the old, debilitated plant. It is no use trying to get such plants to recover, as, when once this disease or weakness begins, it cannot easily be stopped.