The lecturer alluded to the difference existing in plants, not only differences in form, size and, color, but also in other respects, some being hairy, glutinous, sticky, &c. These may be accounted for in a great measure by the relations borne by plants to insects, the visits of which are generally necessary to ensure the fertilization of one flower by the pollen of the other. In some cases, however, such as that of Drosera, the object of the flower is to attract insects for the purpose of devouring them, and therefore the leaves are covered with sticky hairs, which bend gradually forward when an insect alights on the leaf, and squeezes it slowly to death, its juices going to the nourishment of its alluring and deceitful foe.
It is easy to see the advantage which flowers gain from secreting honey, inasmuch as they are dependent for fertilization on the visits of bees and other insects, which while feeding necessarily dust themselves with pollen, and thus carry it from flower to flower. But it is less easy to understand why honey should be secreted on those parts of flowers where no pollen exists, at the base of the leaf-stalks, for instance. For the explanation of this we are indebted to Mr. Bell, and Mr. Delphine, who observed that in some cases upon the stems, and living upon the honey, exist colonies of small ants, constituting a most efficient body-guard against the attacks of leaf-cutting ants. They also protect plants from the attacks of many other enemies, and are in their turn made use of by various small species of Aphides who, by secreting a sweet fluid, of which they allow the ants to avail themselves, convert them from enemies into friends and thereby secure a cordial, instead of an angry reception.
Harmless, however, and even useful as are ants which confining themselves only to the stalks of flowering plants, they would generally be positively injurious to the flowers themselves, as these would merely rob them of their honey without repaying the debt by carrying the pollen to others. Flowers therefore have been driven to protect themselves by various devices, such as slippery surface, sticky glands or hedges of hairs, which entirely prevent the ants from obtaining access to the nectary. For the visits of ants to flowers would not only deprive them of their honey, but would prevent the visits of those insects which are so necessary to cross-fertilization. The instance of the mode in which the common Fox-glove excludes the entrance of ants was given; the flower is a close box, which contains the anthers, pistil and honey. It has the specialties of a flower which is adapted for cross-fertilization by insects, color, honey, and the arrangement of stamens and pistils, but it is closed. The flower is adapted to cross-fertilization by bumble-bees, and they alone can force open the box; to other insects it is closed. Again, the beautiful rosy flowers of the Polygonum Amphibium are rich in nectar, and quite unprotected from the visits of creeping insects so long as the plant is grown in water; the arrangement of the stamens and pistils is such that it cannot fail of cross-fertilization on the visit of any flying insect. When, however, this plant is grown on land, and consequently liable to the visits of creeping things, certain hairs terminating in sticky glands are thrown out, effectively barring the entrance of these worse than useless guests. The so called “sleep” of plants is another means of self-defence adopted by those flowers whose fertilization is dependent upon the visits of day insects; while on the other hand there are other species of flowers adapted for moths and nocturnal insects, which expand towards night, and scent the evening air with delicious perfume. The curious life history of Silene Nutans was then referred to, and the advantages of early rising shown in those flowers which expand early in the morning to receive bees, but close again before the later rising ants are astir.
Sir John proceeded to discuss the means by which insects provide themselves with means of concealment, by imitating the appearance of plants; the “walking stick” insect, and many larvæ are cases in point. Some caterpillars, living on the under side of leaves, not only adapted their color to those leaves, but actually, as their growth increased, altered their markings so as to coincide with the fibres of the leaves. Curiously enough, sometimes bright and striking colors were used as a mode of protection. In these cases, however, they are accompanied by an unpleasant smell and taste, so that the gorgeous dress which would seem so dangerous is in fact a most effectual shield.
The lecturer pointed out that there were five principal types of coloring among caterpillars. Those which live inside wood or leaves or underground are generally of a pale uniform hue; the small leaf-eating caterpillars are green, like the leaves on which they feed. The other three types may “si parva licet componere magnis” be compared with the three types of coloring among cats; there are the ground cats, as the lion and puma, which are brownish or sand color, like the open places they frequent; so also, caterpillars which conceal themselves by day at the roots of their plant food, even if originally green, tend to assume the color of earth. The spotted or eyed cats, such as the leopard, live among trees, and their peculiar color renders them inconspicuous, by mimicking the spots of light and shade among the foliage. Lastly, there are the striped cats, as the tiger, which inhabit the jungle, whose markings render them difficult to see among the brown grass they frequent. The stripes of the tiger are transverse because he walks horizontally on the ground; while the stripes on the caterpillar are either longitudinal or oblique, the direction of the lines follows those of the foliage; those caterpillars which cling to the grass in a vertical position have longitudinal lines, while those which live on mere leaves have oblique lines, corresponding with the oblique midribs of the leaves.
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THE BLACKBERRY.
This fruit has received the least attention at the hands of fruit growers of any of our small fruits. Plants are seldom inquired for, and only a few hundreds are planted, where thousands of currants, raspberries, and gooseberries, and millions of strawberries are set out. Mr. Parry, of New Jersey, is an extensive cultivator of small fruits, and for many years boasted a large number of acres of blackberries under cultivation, and may therefore be considered good authority on the cultivation of this fruit. In a paper read before the Pennsylvania Fruit Growers’ Society, at its meeting in January, 1877, he states that this fruit has sold readily in his markets at from twelve and a half to fifteen cents per quart. The average received by him during the past fourteen years is fourteen cents per quart, and the yield two thousand two hundred quarts per acre.
The varieties to which he gives the preference are Wilson’s Early, Dorchester, Kittatinny, and New Rochelle. The Hoosac Thornless he finds to have no other merit than its freedom from thorns; and the Crystal White, Col. Wilder, and Dr. Warder, with all white, red, and purple blackberries, prove to be unprofitable. Sable Queen, Sinclair, Holcomb, Cumberland, and many other varieties have been tested and found not to be as valuable as the four sorts above named. He has found the Snyder to be remarkably hardy and very productive, qualities which make it very valuable in many localities, because it can be relied upon to produce a full crop, but the fruit is smaller. Clarkson’s Early promises to compete successfully with Wilson’s Early, ripening as soon, and very productive, with fruit of fair size. The Delaware is a very large and excellent blackberry, ripening at the same time with the Kittatinny, and the bush a very vigorous grower, and seemingly perfectly hardy.
The blackberry should not be planted on very rich soil, lest the result prove to be a large growth of canes and very little fruit. After experimenting with many soils, from a firm clay to a light blowing sand, Mr. Parry gives the preference to a light moist sandy loam, and if water would otherwise stand near the surface that which has been thoroughly underdrained. He states that a fruit grower who had forty acres devoted to the growing of blackberries bought a tract of light sandy land at thirteen dollars per acre, and planted it with them; but in order to have a model patch he purchased a few acres of the best and richest land in the vicinity, at three hundred dollars per acre, and planted it with the same kind of blackberries, gave it the best of care, obtained an immense growth of canes; but never as much fruit as from the cheaper land.