168 STEMS 
production, for a well branched tree can produce more flowers and 
fruit than one that is less branched, provided the food supply is 
sufficient. In plants used for forage, such as Clover and Alfalfa, 
the amount of hay produced by a plant depends largely upon the 
extent of branching. 
In some plants, as in the Pine shown in Figure 145, the stem 
system consists of a main axis and many lateral branches, forming 
a what is known as the excur- 
rent type of stem. In others, 
as in the Elm shown in 
Figure 146, the main stem is 
divided into two or more 
branches, which are soon lost 
in numerous branches, form- 
ing the deliquescent type of 
stem. Among fruit trees and 
forest trees, there is so much 
difference in habits of branch- 
ing that many kinds of trees 
can be identified by their 
branching habit. 
Work Done by Stems. — 
There are four important 
functions of stems. They 
support the aérial structures, 
conduct materials, make 
food, and serve as regions of 
storage. 
The supporting function 
Fro. 146. —Elm tree, showing dei  COMSiSts in carrying the 
AieMentceype.at eeu weight of the leaves, flowers, 
and fruit, and in elevating 
them to a position most favorable for performing their func- 
tions. There is strong competition among plants for light, and 
it is through the elongation of the stem that plants lift their 
leaves higher in the air and often escape the shade of neigh- 
boring plants. Some plants, such as the Grape, Poison Ivy, 
Morning Glory, Beans, and Peas, which have weak stems, secure 
better light by climbing a support, such as a wall, fence, or the 
stems of other plants. 
