Page:Popular Science Monthly Volume 35.djvu/544

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WHILE, as Darwin and his successors have established, plants are dependent to a considerable extent upon insects for the means of securing the fertilization of their seed, they are also liable to be eaten by them, and are in great danger from the voracious appetites of other animals. They are not, however, wholly without defense against these attacks, but are provided with armors of various kinds, by the aid of which they offer a more or less effective resistance to them. These methods of defense have been the subject of special investigation by Prof. E. Stahl,[1] of the University of Jena, whose work, "Pflanzen und Schnecken" (June, 1888), presents a most interesting chapter in the history of the vegetable struggle for existence.

While every plant has its enemies more or less numerous and dangerous, the number as a whole is not generally considerable. Some attack the young plant, others the adult; some one part of it, some another. They would, perhaps, be more numerous were it not for the effectiveness of the means of defense that the plant can present against them. These means are various, but without them vegetable species would disappear very quickly. The protection conferred by them is evident, but an enemy more or less is much for a plant. It is sometimes a question of life or death. The phylloxera alone has been competent to destroy the vine in France; and, if ruminants should add their attacks to those of insects against the thyme or euphorbia, those kinds would soon disappear. In some cases, as of thorns or nettles, the armor is easily discovered; in other cases it is internal, chemical, or toxic. The protection is evident, whatever its nature may be. The question arises whether it is fortuitous or the result of a selection among plants. We can hardly doubt what the answer should be. Selection has certainly played a considerable part in the matter.

  1. Prof. Stahl's study is not the only one that has been made in this line, although it is perhaps the only experimental one. M. L. Erréra, of Brussels, presented a short memoir to the Royal Botanical Society of Belgium in 1886, in which he pointed out how experiments and observations could be carried on in reference to the subject. He drew up a table in which he classified the means of defense presented by plants as follows:—Biological characters: Plants at stations not easily accessible or with organs difficult of access, social plants, vassal plants, bullying plants (simulating dangerous species). Anatomical characters: Hard, cutting, or piercing organs, calcification, silicification, nettle-hair?, thorns, etc. Chemical characters: Acids, tannins, volatile oils, bitter properties, alkaloids, and glycosoids. M. Erréra adds a table of plants known to him which present one or another of the characteristics thus described. But his design was simply to show how great an interest the study might be made to afford. His views are confirmed by Prof. Stahl's researches.