286 ORGANIC AGRICULTURAL CHEMISTRY 



Protein Content of Crops. — The protein content of some of 

 the different crops is given in the preceding table. The figures 

 represent crude protein as determined by multiplying the 

 nitrogen per cent by the factor 6.25. This includes, with the 

 proteins, the amino-acids, but these are not of any large amount 

 except in the cases of green crops and root crops and in malt 

 sprouts. 



AMINO-ACIDS, ALKALOIDS, ESSENTIAL OILS, TER^ 



PENES, TANNINS, ETC. 



We have thus far discussed the occurrence in plants of the 

 three essential organic food constituents together with a few 

 related compounds of industrial or physiological importance. 

 These are by far the most important plant constituents, es- 

 pecially from an agricultural viewpoint, for plants considered 

 agriculturally are chiefly used as food. When not used as 

 food they are generally used for the manufacture of valuable 

 products. All of these uses have been as fully considered as 

 is desirable. 



There remain, however, several groups of substances found in 

 plants which are of considerable importance. 



End Products of Metabolism. — In animal metabolism pro- 

 teins are broken down by the katabolic process into simpler 

 compounds with the liberation of energy. The nitrogen-con- 

 taining compounds which are thus formed are carried off in 

 the urine, as true excretion products, in the form of urea and 

 related compounds. In plants protein cell food is probably 

 katabolized in a similar way, but the nitrogen-containing prod- 

 ucts are not cast off from the plant as true excretion substances. 

 It is possible that amino-acids are excreted as such, but in many 

 cases these amino-acids or other complexes derived from the 

 protein molecule are not excreted, but are further metabolized 

 into end products which remain in the plant. Such charac- 

 teristic compounds as caffeine, theobromine, strychnine, morphine. 



