24 THE SMALL GRAINS 



dermis. The mesophyll is made up chiefly of spongy 

 parenchyma and is abundantly supplied with chloroplasts. 

 The border parenchyma is a sheath surrounding each 

 extension into the leaf of a fibrovascular bundle. There 

 are many large intercellular spaces in the spongy paren- 

 chyma that intercommunicate freely and connect with 

 the stomata (Fig. 3). 



25. Translocation and assimilation. It will now be 

 easy to understand the entire elaboration and transloca- 

 tion of food materials : from the soil, water and soluble 

 salts are absorbed into the roots through the root-hairs 

 and are thence conducted through the fibrovascular 

 bundles into the leaves. Here there is a constant supply 

 of carbon dioxide from the air, through the stomata and 

 intercellular spaces, which, with the water in the paren- 

 chyma cells (delivered thereto through the border paren- 

 chyma from the nearest bundle) enter into the formation 

 of sugar, starch, or other carbon compounds, by the energy 

 of the sunlight, in the presence of the chlorophyll existing 

 in these cells. It should be stated that this action may 

 also take place in the border parenchyma itself. 



The mineral salts from the soil combine with nitrogen 

 and carbon compounds to form amides or other nitroge- 

 nous materials. 



After making use of a portion of these foods in actual 

 assimilation, or leaf construction, and retaining other 

 portions as cell contents (oils, mineral crystals), the re- 

 maining soluble or diffusible portions, such as sugars, 

 oils, and amides, are translocated to other portions of 

 the plant, being delivered through the border parenchyma 

 into the bundle, the tracheids of which carry the water 

 and small portions of food materials, and the sieve tubes 

 carry the bulk of the soluble foods, On reaching their 



