62 



THE VEGETATIVE FUNCTIONS OF PLANTS 



general types of distribution will be recognized, repre- 

 sented respectively by the corn or the lily, and by the 



castor-oil plant or the parsnip. 



61. Internal Structure of the 

 Corn Stem. In the corn stalk, 

 the nbro-vascular bundles are dis- 

 tributed thickly and irregularly 

 through the fundamental tissue 

 (parenchyma) of the stem (Fig. 45). 

 They are somewhat more numerous 

 near the outer rind. A longitudi- 

 nal section shows the bundles in side 

 view, extending through the stem. 

 The corn stalk represents a type 

 of structure (monocotyledonous) 

 common to all grasses 1 and closely 

 related plants, and often, though 

 misleadingly, called endogenous. 

 Ingrowth, the new tissue originates 

 (with few exceptions, e.g., Yucca) 

 only at the tip of the stem. As a 

 rule, growth in thickness results 

 only by the enlargement of cells 

 already formed, without involving 

 the formation of new ones. 



62. Internal Structure of the 

 Castor-oil Plant Stem. A type 

 of structure quite different from 

 that of the corn stalk is illus- 

 trated in the stem of the castor-oil plant (Fig. 46) . Here 

 the nbro-vascular bundles (in the young stem) are 



1 The Indian corn (maize) belongs to the family of Grasses (Graminese). 



FIG. 45. Fibro- vascular 

 bundles in a corn stalk (Zea 

 Mays). 



