178 STEMS 



borne. In most cases aerial stems are produced, and the leaves 

 of the underground stem are mere scales. 



Although the underground stems are the least adapted for leaf 

 display, they have some advantages that aerial stems do not have. 



Fig. 153. Smilax climbing over bushes by means of tendrils. 

 After Kemer. 



They are much less exposed to drying and freezing, and escape 

 being pastured off by stock. They are safe places for the storage 

 of food, and most underground stems do have much reserve food, 

 which is used in the growth of new aerial shoots at the opening of 

 each growing season. Herbaceous plants are able to persist for 

 many years, if they have an underground stem from which new 

 shoots may arise each year. In other words, an underground 

 stem is one of the features that makes it possible for herbaceous 

 plants to be perennials. The underground position is an advan- 

 tageous one for vegetative propagation, because not only are the 

 nodes favorably located for estabUshing roots, but the supply of 

 reserve food and protection from drying and freezing makes it 

 possible for even small segments of underground stems to live 

 and develop separate plants. When an underground stem like 

 that of Quack Grass is hoed to pieces, each segment, if it has a 



