NUTRITION 85 



and method of their formation have never been clearly 

 determined. 



85. Digestion. — We have learned above (paragraph 42) 

 that substances can enter a plant only in solution. It is 

 also true that substances, even when inside the cell, can- 



FlG. 62. — Portion of a cross-section of a grain, of Indian corn {Zea 

 Mays). G.E, Glandular epithelium of the scutellum which secretes dias- 

 tase; G, a simple racemose gland in the tissue of the scutellum; D, duct of 

 the latter, empt3ang into the starchy endosperm surrounding the embryo. 

 (Photomicrograph by the author.) 



not be utiKzed as food by the plant unless they are in 

 solution. In order that the protoplasm can be nourished, 

 therefore, all insoluble stored foods must be converted 

 into soluble substances and dissolved. The process of 

 converting an insoluble food into a soluble substance and 

 dissolving it is digestion. This change, like the various 

 processes in photosynthesis, is brought about by various 



