XEROPHYTE ASSOCIATIONS. 



207 



tance in xerophytic conditions. In 

 the cactns plants the peculiar stems 

 have become great reservoirs of 

 moisture. The globular body may 

 be taken to represent the most com- 

 plete answer to this general problem, 

 as it is the form of body by which 

 the least amount of surface may be 

 exposed and the greatest amount of 

 water storage secured. In the case 

 of fleshy leaves and fleshy bodies it 

 has long been noticed that they not 

 only contain water, but also have a 

 great power of re- 



Fig. ISO. A fragment of bar- 

 berry, showing the thorns. 

 — After Kernteb. 



Fig. 181. Twig of com- 

 mon locust, showing 

 the thorns. — After 



Kekner. 



15 



taining it. Plant 

 collectors have found much difficulty in 

 drying these fleshy forms, some of which 

 seem to be able to retain their moisture in- 

 definitely, even in the driest conditions. 

 155. Xerophytic structure. — The adap- 

 tations given above are generally found 

 in plants growing in drouth conditions, 

 and they all imply an effort to diminish 

 transpiration. It must not be supposed, 

 however, that only plants living in 

 drouth conditions show these adapta- 

 tions. Such adaptations result in what 

 is known as the xerophytic structure, 

 and such a structure may appear even 

 in plants growing in hydrophyte condi- 

 tions. For example, the bulrush grows 

 in shallow water, and is a prominent 

 member of one of the hydrophyte asso- 

 ciations (see §13?) ; and yet it has a re- 

 markably xerophytic structure. This is 

 probably due to the fact that although it 



