106 



BOTANY 



and of the Loasaceae, are special forms of bristles, and arise as 

 prolongations of single epidermal cells. These, however, swell in 

 the course of their development, and becoming surrounded by 

 adjoining epidermal cells present the appearance of being set in 

 sockets ; while, at the same time, by the multiplication of the cells 



FIG. 115. Seed-hairs of the cotton, Gossypium her- 

 baceum. A, Part of seed-coat with hairs (x 8) 

 BI insertion and lower part, B% middle part, and 

 83 upper part, of a hair, (x 300.) 



Fio. 116. Stinging hair of Urtica 

 dioica, with a portion of the epi- 

 dermis, ami, to the right, a small 

 bristle, (x (X).) 



in the tissue at their base, the whole hair becomes elevated on a 

 column-like protuberance. The hair tapers towards the apex and 

 terminates, somewhat obliquely, in a small head, just below which 

 the wall of the hair remains unthickened. As the wall of the hair is 

 silicified at the end and calcified for the rest of its length, the whole 

 hair is therefore- extremely stiff. Such hairs furnish a means of 

 defence against animals. The heads break off at the slightest touch, 

 and the hairs piercing the skin pour out their poisonous contents, 



