320 A TEXT-BOOK OF BOTANY. 



II. THE OUTER MORPHOLOGY OF THE STEM. 



The stem, or ascending axis of the plant, usually grows in a 

 direction opposite to that of the root, seeking the light and air. 

 The tendency of the stem to grow upward is characteristic of 

 the majority of plants, and is spoken of as negative geotropism. 

 The growing point of the stem is at the apex, and it is protected 

 by a layer of bud scales (Fig. 179, B). 



Fig. 178. Longitudinal section through a root of Veratruyn viride showing the nature 

 of the contraction of the root: E, epidermis; CS, cells of cortex containing starch; CO, 

 cells of cortex containing raphides; F. hbro vascular bundle; A, rifts or cavities formed as 

 a result of the radial swelling of the cells of the cortex. 



Stems are further characterized by bearing leaves, or modi- 

 fications of them. The leaves occur at regular intervals in the 

 same species, and that portion of the stem from which they arise 

 is spoken of as a node, while the intervening portion is called an 

 internode. 



Stem branches usually arise in the axils of the leaves, first 



