72 



PRINCIPLES OF PLANT CULTURE 



N 



\ 



THE STEM 



113. The parts. As the root develops from the base 

 of the hypocotyl, the plumule, or primary shoot (55), 

 develops from the other end and becomes, at least for a 

 time, the main axis or stem. 



114. The stem is, generally 

 speaking, the part of the plant that 

 supports the leaves. In excep- 

 tional cases, as in the potato 

 (Fig. 34) and quack-grass, a part 

 of the stem grows beneath the 

 ground, on which the leaves usu- 

 ally do not develop (underground 

 stems) ; and in a few plants, as in 

 some cacti, the stem performs the 

 whole office of leaves. The stem 

 may be strong enough to support 

 its own weight, as in trees and 

 shrubs, or it may depend upon 

 other objects for its support, as in 

 vines. 



115. Nodes and internodes. - 

 Unlike the root, the stem is de- 

 veloped in successive sections, 

 comparable in part to the stories 



of a building. Each section or story consists of one or 

 more leaves, attached to the distal end of a part of 

 the stem. (Distal means farthest from the point at 

 which growth started. It is opposed to proximal, which 

 means nearest the point of origin.) The part of the 

 stem to which the leaf or leaves are attached is called 

 a node and the part below the node, or in the stem as 



FIG. 35. Nodes (N) ; A, 

 of the box elder, Acer 

 Negundo; B, of the wild 

 grape, Vitis riparia. 



