94 



HISTOLOGY AND PHYSIOLOGY. 



In Mosses, hairs, called rhizoids (Gr. rliiza, root), perform 



the function of roots ex- 

 clusively, the latter being 

 absent in these plants. 

 In many hairs on aerial 

 parts of plants, the ter- 

 minal cell, or cluster 

 of cells, becomes trans- 

 formed into a secreting 

 organ, in which gummy, 

 resinous, or other substances are produced. These are 

 termed glandular hairs (Fig. 210, gl). Related to these 

 are the hairs of some Thistles, with elongated lashes. 

 The leaves of the Sundew (Drosera) have stalked, sensitive 

 glands, for the capture of insects upon which these plants 

 partially feed. 



120. The stomates (Gr. stoma, mouth) are minute ori- 

 fices (Figs. 211, 212) in the epidermis, surrounded by two 

 chlorophyll-bearing cells, called guard-cells (Fig. 211, g). 

 Immediately under each stomate is an air cavity (Fig. 212, 

 a). Stomates are never present in roots,' seldom in sub- 

 merged or underground stems; but exceedingly numerous on 

 aerial stems and leaves. ^ ,i 



They are also met with 

 at times on sepals, petals, 

 and carpels of flowers. 

 As a rule, they are more 

 numerous on the lower 

 than on the upper side 

 of the leaf. On the upper 212 



Fip. 2]1. Epidermis of Potato leaf, showing stomates (si) and guard-cells (g). 

 Fig. 212. Section through the epidermis and stomate (si) of Potato leaf: a, sur 

 cavity. 



