XEKOPHYTES AXD HALOPHY I'ES. 



323 



ada[)tations to reduce evaporation. In the lea\'es of some 

 xeroi)hytes the guard tells of tlie stomata are motile only 

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

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





Fig. 365. 



Fig. 367. 



Fig. 366. — Portion of a tnins^'erse section throngh a node of sugar-cane, sliowing rods 

 of wax secreted by tjie epidermis. Magnified 142 diam. — After De I^arj'. 



Fig. 367. — Transverse section of a portion of tlie margin of a leaf of Aloe so^otrnia. 

 c, tliick cuticle ; below <:, cutinized layers of wall of epidermis, ej> ; /, parenchyma 

 cells with cbloroplasts ; cr, a crystal cell with needle crystals of oxalate of lime ; s/>, 



fuard cells of stoma, stink below surface ; a, intercellular space under stoma. Magni- 

 ed about 175 diam. — After Tschircli. 



(b) The inlenial tissues of the leaves may be more compact. 

 This reduces transpjiration bv restricting the area of the air 

 passages. Such dense structure is secured by multiplying 

 the number of the palisade la\'ers and by the more regular 

 form of the spongy p)arench3-ma (fig. 359 and •" 167). 



B. Adaptations for taking up water. 



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

 mediate absorj.ition of moisture in the air or of liquid water 

 falling on their aerial parts. Such are, usuallv, the 

 alg£e, lichens, and mosses which grow in exposed situations. 

 2. Certain of the higher pilants are furnished with hairs 

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



