DIV. I 



MORPHOLOGY 



55 



freely projecting body of the hair. The epidermal cells around the 

 base are often arranged in a ring or radiate on all sides, and may 

 be called the subsidiary cells of the hair. The STINGING HAIRS 

 (Fig. 55), such as those of Nettles (Urtica) and of the Loasaceae, are 

 special forms of bristles. 



They arise from single epidermal cells which 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 multi- 

 plication of the cells in the tissue at 

 their base, the whole hair becomes 

 elevated on a column-like protuber- 

 ance. 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 extremely stiff. 

 The heads break off at the slightest 



B. 



FIG. 52. Seed -hairs of the cotton, Gossypium her- 

 baceum. A, Part of seed-coat with hairs (x 3). 

 B lt Insertion and lower part, -Bo middle part, and 

 B 3 , upper part, of a hair. ( x 300. After STRAS- 



BCRGER.) 



FIG. 53. Stellate hair in surface view from the 

 lower epidermis of the leaf of Matthiola 

 annua. (x 90. After STRASBURGER.) 



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

 especially in the case of some tropical nettles, may cause severe inflammation. 

 According to G. HABERLANDT this is due to the presence of a toxin of albu- 

 minous nature. 



Hairs have thus various forms and perform very different functions. 

 They frequently contribute to the protection afforded by the epidermis, 

 forming a covering to full-grown parts of the plant and very 

 frequently to the young parts in the bud or expanding from this. 

 Such coverings, which may be composed of dead woolly hairs, serve 



