HOW PLANTS GROW 11 



shown later, the incomplete proteins may have a lower value for 

 animal feeding than those which are complete. 



During the growth of the plant, amids are constantly being formed 

 in the living cells out of sugar or starch and the nitrates and other 

 mineral salts. These amids are continually being carried to needed 

 points and there changed into the proteins, and as a consequence do 

 not usually accumulate in the plant. Just as starch and sugar are 

 changed one into the other in the plant, so the proteins and amids 

 may be changed one into the other as plant necessity may require. 

 When germination starts in a seed, an enzyme, or ferment, it contains 

 acts on the insoluble proteins stored in and about the germ and 

 changes them to soluble amids, so that the nitrogen may be trans- 

 ferred to the newly forming parts of the plantlet. But little crude 

 protein is found in the older, woody parts of plants, the greater por- 

 tion always being concentrated at the points of growth; i. e., in the 

 leaves, flowers, and seeds. 



Plants support animal life. — It is Nature's plan that plants shall 

 use energy supplied by the sun in building inorganic matter taken 

 from earth and air into organic compounds. In this process the sun 

 energy employed becomes latent, or hidden. Animals can not directly 

 secure from the sun the energy necessary for their life but must 

 live on the organic compounds built by plants. After more or less 

 change during digestion, these compounds are built into their body 

 tissues or are broken down within their bodies to produce heat and 

 energy. In the coal burning in the grate, there reappears the energy 

 of the sun which was stored in the plants of ages ago. In a similar 

 manner the energy received from the sun by plants during their 

 growth is transformed into animal heat and energy. Plants are thus 

 sun-power machines for furnishing food to support animal life. 



II. How the Chemist Groups Plant Substances 



As we have seen, many different compounds are formed in plants, 

 some of these being so complex that their exact structure has not yet 

 been determined. In studying feeding stuffs it is desirable to group 

 all plant compounds into a few classes, the amounts of which can be 

 readily found by chemists. Accordingly, in analyzing plant materials 

 and feeding stuffs, the following classes or groups of substances are 

 commonly determined : water, ash or mineral matter, crude protein, 

 fiber, nitrogen-free extract, and fat. The average percentages of 

 these in typical feeds are shown in the following table, which is taken 

 from Appendix Table I. The last column gives the number of 

 analyses from which the average composition has been computed by 

 the authors. 



