ASSIMILATION OF FOOD 



193 



which help to digest the reserve food in the endosperm, and the 

 same thing occurs in the date palm (Fig. 104). 



Glands devoted to the secretion of enzymes occur in Dro- 

 sera, Dionaea and Nepenthes (Fig. 105), but in these instances 

 the enzymes do not act upon food stored within the plant, Init 

 upon insects, and the glands are comparable 

 to those in the alimentary canal of animals. 



It seems that the enzymes do not reach the 

 maximum amount in the cells until the process 

 of digestion is well started, and it is for this 

 reason that more diastase can be extracted 

 from sprouted than from unsprouted barley. 

 The mere presence of the enzymes is, how- 

 ever, not enough to start digestion going; 

 rather the impulse to grow and the actual 

 inception of growth creating a demand for 

 food seems to supply the stimulus that puts 

 digestion in motion. Such procedure would 

 of course be a vital one initiated by the living 

 protoplast. 



Assimilation of Food. — We must keep in mind the fact 

 that the proteids, oils, starches, sugars, and other kinds of food 

 have two distinct uses: to furnish chemical elements for the 

 construction of the protoplasts and cell-wall, and other special 

 and useful products, such as nectar, aromatic oils, and enzymes, 

 and to supply energy in the form and place needed to keep the 

 vital machinery in motion. That food which is taken on by the 

 protoplast and made a part of its own body is assimilated. We 

 say that the food is lifeless but the protoplast is living. Neces- 

 sarily the food passes from the lifeless to the living condition by 

 something that the protoplast does with it. In this process the 

 food loses its identity. Sugar, oil, soluble proteids, etc., enter 

 into new combinations resulting in the formation of protoplasm — 

 the living substance. An attempt to explain how this most 

 wonderful of transformations takes place would be the merest 

 speculation. We know nothing profoundly about it. To 



Fig. 105.— Longitu- 

 dinal section through 

 a digestive gland of 

 Drosera rotundifolia. 

 (After de Bary.) 



