CHAPTER IX. 



THE STEM. 



118. Definition. — The shoot is almost always segmented 

 into members of two kinds, the stem and leaves. The stem 

 is the central axis of any shoot, and the leaves are lateral out- 

 growths, or branches, of it. These two members cannot be 

 accurately defined, but are in most cases readily distinguish- 

 able. Leaves commonly differ from the stem in internal 

 structure, and in their flattened form, limited growth, and 

 position, subtending the lateral shoots. (See further p. 117.) 



119. Nodes and internodes. — Upon examining the surface 

 of the stem, it is almost always readily distinguishable into 

 distinct regions, the nodes and internodes. The nodes are 

 the narrow zones, often somewhat swollen (whence the name), 

 at which one or more leaves arise. The internodes are the 

 zones between the nodes. Upon watching the development 

 of the stem from the terminal bud, it will be seen that new 

 nodes and internodes are constantly emerging from its base, 

 and that the leaves formed at the nodes are successively 

 expanding. This emergence of the internodes is due to their 

 elongation. The amount of elongation, however, varies 

 greatly in different plants, and even in different parts of the 

 same plant. In many cases the internodes are considerably 

 and uniformly elongated ; the leaves are then distributed 

 along the stem at considerable and regular intervals. In other 

 cases the internodes remain very short, and the leaves are, 



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