IX] FLESHY LEAVES 129 



Many other plants of arid regions meet similar con- 

 ditions of existence by having more or less succulent 

 internodes or stems, and transient, small or no leaves, e.g. 

 species of Senecio, Sarcocaulon, Salicornia. 



But in many cases, such as Aloe, Agave, Crassulaceae, 

 Gasteria, &c., the succulence is transferred to the leaves, 

 which become correspondingly stout and fleshy, and have 

 thick cuticles and few or protected stomata, while the axis 

 undergoes no essential modification. In a certain sense, 

 and bearing in mind the super-terranean habit and that 

 the chief point in succulent shoots is the storage of water, 

 we may compare Cactiform stems with tubers, and these 

 Crassuloid forms with bulbs. 



All transitions occur from shoots with long internodes 

 and merely succulent leaves otherwise little altered — 

 e.g. Inula crithmoides, Crithmum maritimum, Cotyledon 

 umbilicus, Sedum Telephium, species of Senecio, &c. — to 

 forms with short internodes and extremely fleshy leaves, 

 reduced in surface to cylindrical or other simple shapes, 

 and forming closely crowded rosettes, as in many species 

 of Crassula, Sedum, Mesendjryanthenium, Portulacace£e, 

 Aloe, Haivorthia, Gasteria, Agave, Fourcroya, &c. 



[Spiny and thorny shoots, also green assimilating 

 stems, including cladodes, have been discussed in Vols, 

 I. and II.] 



W. V. 



