52 PLANTS 



III. Other types of underground storage stems are common. 

 The root-stock dilTers from the tuber in that it has no slender 

 connecting stem but is thickened throughout its length. It 



Fig. 24. — Young shoots of the common cactus, Opuntia, showing the small, 

 conical leaves. These soon disappear. Note that the spines develop in the 

 axils of the leaves. X2/3. 



usually persists from year to year; a new segment consisting 

 of one or more nodes, being added each season. When the 



