58 



DICOTYLEDONS 



green and does the work of the leaves in tlie preparation of 

 starch from the air. The moisture, of wliich the plant gets a 

 very scanty supply, is stored up, as in a reservoir, in the fiesliy 

 parts of the stem and evaporated very frugally, the epidermis of 

 it being thick and almost water-tight, the stomata in it being 



Fig. I. — The' Niglit-flinvcrins" Cactus {Ccreiis (jran(Ullo)its). 



very few, and the sap l)e('oiiiing a tliiek and slimy tluid which 

 <loes not easily pass into vapour. Thus the plants arc al)le to 

 thrive even when everything around them is dried up. lieiiig 

 the only sueculcnt things in the deserts in which they grow wild. 



