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 

 r-^ — - what is known as the excur- 



rent type of stem. In others, 

 . . as in the Elm shown in 



Figure I46, 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 aerial structures, 

 conduct materials, make 

 food, and serve as regions of 

 storage. 



The su]) porting function 

 consists in carrying the 

 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. 



Fig. 146. — Elm tree, showing deli- 

 quescent type of stem. 



