442 PROTECTION OF GREEN LEAVES AGAINST ATTACKS OF ANIMALS. 



itching, and very severe attacks, tetanus, &c. are produced, as by snake-bites, 

 by the Urtica stimulans of Java, the Urtica crenulata, which is a native of 

 India, and the Urtica Tnentissima, growing in Timor. Generally, an analogy 

 between stinging hairs and the hollow poison-fangs of snakes cannot fail to be 

 recognized. 



The mass of tissue in which the stinging hair is imbedded consists of chloro- 

 phyll-bearing cells, and is elastic and flexible; whenever a stinging hair is pressed 

 on one side it lies close to the leaf-surface, so that the point does not penetrate 

 the skin of the fingers pressing it, and does not form, or poison, a wound. When 

 the pressure is removed, the hair becomes erect again in virtue of the elasticity 

 of its knob-like support, and directs its brittle point outwards. Upon this fact 

 depends the trick of stroking a nettle with the hand so as not to be stung. The 

 lower, unarmed part of a leafy nettle, whose foliage is beset with innumerable 

 projecting stinging hairs, is taken in one hand, and the other hand is then passed 

 from below upwards over the foliage, and in this way the hairs touched are 

 pressed on to the leaf surfaces and do not wound. But if the nettle is touched 

 from above, the heads of the hairs are immediately broken ofi", the perforated 

 points penetrate the sk'u and discharge their poisonous fluid into it. Grazing 

 animals carefully avoid plants furnished with stinging hairs, and do not let 

 their nostrils, nor the mucous membrane of their mouths, get poisoned by the 

 corrosive fluid. The nettle is, therefore, well protected against larger animals. 

 Their foliage is, indeed, eaten by the larvae of Vanessa Urticce in spite of the 

 stinging hairs, but this injury is restricted to only a portion of the leaves; they 

 can always develop new leafy shoots from the intact stems and buds, and, at 

 any rate, the nettle does not perish on account of the ravages of these larvae. 



This is also the most suitable place for the consideration of a form of plant- 

 hair, whose cells, indeed, possess no stiff" silicified walls, and which, therefore, 

 do not prick and wound, but which, nevertheless, keep the plants they clothe 

 from injury by grazing animals, and which thus far must also be regarded as 

 agents for protecting the green tissue. These hair-structures have already been 

 described when making clear the protection afforded to leaves against excessive 

 transpiration. Such hairs, as we saw, are particularly well shown by many 

 species of the genus Mullein (Verhascum). These branched, radiating hairs, 

 reminding one of tiny fir-trees, are easily detached from the surface of tlie 

 leaves from which they spring, and a very slight pressure of the hand is sufficient 

 to lift off numerous flocks of this hair-felt. Although the cells which build up 

 the hairs of the leaf-felt are not stiff" and prickly, and do not penetrate into 

 the skin, they very readily remain hanging to the smallest inequalities on the 

 surface of the disturbing body. If grazing animals bring the mucous membrane 

 of their mouths into contact with the leaves of the Mullein, this mucous membrane 

 immediately become covered with flocks of the detached hair-felt, which establish 

 themselves in the inequalities of the surface, and they certainly produce anything 

 but a pleasant sensation. On the peculiar adhesion of the felt-hairs of the 



