XEROPHYTES AND HALOPHYTES. 



323 



,ni1-ipfntjnnc tp r^dll^w^yapnrririrm In the leaVCS of SOUK' 



xerophytes the guard cells of the stomata are motile only 

 when young, becoming thick-walled and fixed when the leaf 

 is mature. The stoma itself sometimes becomes closed, also. 



Fig. 366.- -Portion of a transverse section through a node of sugar-cane, showing rods 

 of wax secreted by the epidermis. Magnified 142 diam.— After I »e Bary. 



FlG. 367. — Transverse section of a portion of the margin of a leaf of Aloe socotrina. 

 1. thick cuticle; below,, cutinized layers of wall of epidermis,*'/; /, parenchyma 

 cells with chloroplasts ; . r. a crystal cell with needle crystals ot oxalate of lime; sp, 



fuard cells of stoma, sunk below surface : .;, intercellular space under stoma. Magni- 

 ed about 175 diam. — After Tschirch. 



_{&L- l'he internal tissues of the leaves may be more compact. 

 This reduces transpirationby restricting thelil'ea of llie-air 

 passa ges. Such dense structure is secured by multiplying 

 th e number of the palisaTrrr iTTycrs and by the "Tub re regular 

 form of the spongy parenchyma (fig. 359 and ^' 167). 



B. Adaptations for taking up water. 



439. Absorption. — 1. Some plants are adapted to im- 

 mediate absorption of moisture in the air or of liquid water 

 falling en their aerial parts. Such are. usually, the 

 algae, In hens, and mosses which -row in exposed situations. 

 2. Certain of the higher plants are furnished with hairs 

 adapted to the prompl absorption of rain or dew, e.g., Spanish 



