24 HORTICULTURE FOR SCHOOLS 



40. The stem. Many kinds of stems are common to 

 plants. Some are herbaceous and consist almost entirely of 

 living tissue; others are woody and consist largely of dead 

 tissue. Stems may be long or short, slender or thick. They 

 may run along the ground as in many vines, or may climb 

 or twine around supports, or may be of such strength as 

 to hold their foliage up into the air and light without 

 assistance. 



41. Structure and functions of the stem. In the young 

 stem, or very young growing portions of older stems, the cells 



I Vascu/ar 

 {Bund/e 



Pith 



FIG. 11. A, Cross-section of very young growing portion of exogenous stem with cells 

 nearly alike. B, An older stem with various tissues developing. 



are much alike. Later they become differentiated. Figs. 11 

 and 12 show the appearance in cross-section of a number of 

 bundles (vascular bundles) in the pith of a stem. The inner 

 side of each bundle consists of various modified cells which 

 later form the woody portion of the plant known as the xylem. 



