The Stems of Plants iii 



Fig. 6o. Sand-reed grass (Ammophila) planted on dunes near Casmalia, California, to 

 prevent further movement of the sand. The bare areas are dunes formed since the planting. 

 The underground stems of the grass bind the sand and aid in preventing its movement by 

 the wind. 



them nearly free from transpiration, from injury by fires (an im- 

 portant matter on the prairies) , and from the destructive effects of 

 winds. Yet when plants having underground stems only come into 

 competition with those having erect stems, they are quite likely to 

 be overshaded ; at any rate they cannot compare with erect stems 

 in leaf display. In competition with annuals, however, they are 

 highly successful by occupying all of the space and thus prevent- 

 ing the young seedling from getting a start. One need only look 

 at the plants in old meadows, pastures, prairies, and swamps to 

 see the result of such competition. 



The commonest type of underground stem is the rootstock or 

 rhizome. Rootstocks are horizontally growing stems, from which 

 the aerial stems arise. They may be slender, or thick and fleshy. 

 Usually they have small scale leaves and buds at the nodes, as 

 well as roots that arise from the nodes or from the entire under 

 surface. The presence of nodes is the external feature of under- 

 ground stems that distinguishes them from roots (Fig. 62). 



