Ecological Types of Stems 



171 



C. J. Chamberlain 



Fig. 97. Giant cereus of south-central Mexico in bloom. This specimen is 35 feet in height ; 

 occasional plants attain a height of 50 feet. In the pulpy interior of a cactus plant of this 

 size IS to 25 tons of water may accumulate. 



those of the cactus type. The stems are covered with cork, 

 heavy cuticle, and sometimes wax and hairs. In the " palo 

 verde " leaves are absent, and the cortex contains chlorophyll. 

 Many of these shrubs have spines and thorns. 



Short-stemmed type. These plants are often called stemless 

 because the leaves occur seemingly at the top of the root. In 

 reality the stem is a disk, or a rounded cone of nodes topping a 

 fleshy root. Internodes fail to develop, and the result is a rosette 

 of leaves, either flattened against the ground as in the evening 

 primrose, or raised and forming a hemispherical group of radiating 

 fleshy or bayonet-like leaves, as in the yucca and agave. Some 



