110 



PART II. ANATOMY AND HISTOLOGY. 



[80 



tvmunentary tissue, and are generally formed each as a,u outgrowth 

 of a single superficial cell (Fig. 90; see also Fig. 31, p. 47; and 

 F'ig. 82, p. 101). 



The hairs of the subaerial parts of plants are, like the epider- 

 mal cells, cuticularised. In many cases the protoplasmic contents 

 disappear at an early stage (as in Cotton, the hairs on the outer 

 coat, or testa, of the seed of Grossypium) and are replaced by air. 

 Sometimes the cell-wall contains deposits of lime or of silica. The 

 hairs are frequently glandular (see p. 100). 



FIG. 90. Hairs on a young ovary of 

 Cucurbits (x 100): b glandular hair ; eef 

 early stages of development. 



wl 



FIG. 91. Root- 

 hairs (h) on the 

 primary root (ic) 

 of a seedling of 

 the Buckwheat : 

 he hypocotyl ; c c 

 cotyledons. 



The root-hairs (Fig. 91 ; also see p. 46) are developed each from 

 a single cell of the piliferous layer ; they are not developed in the 

 immediate neighbourhood of the growing-point, but at some little 

 distance behind it. Moreover, as they grow older, the root-hairs 

 die off ; hence they are only to be found on a very limited region of 

 a primary or a secondary root. 



31. The _ Primary Ground-Tissue is constituted, by the 

 tissue which belongs neither to the epidermis, on the one hand, 

 nor to the stele on the other. 



