178 STEMS 
borne. In most cases aérial 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 aérial stems do not have. 
Fic. 153. Smilax climbing over bushes by means of tendrils. 
After Kerner. 
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 aérial 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 establishing 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 
