PLANT FOOD AND PLANT GROWTH 



39 



Zein, the most abundant proteid in corn (Zea mays), has the 

 following composition: 



Carbon .... 55.15 per cent. 



Hydrogen ... 7.24 per cent. 



Oxygen. . . . 20.77 per cent. 



Nitrogen . . . 16.22 per cent. 



Sulfur .... .62 per cent. 



According to this analysis, the molecule of zein might be repre- 

 sented by the following formula: 



Ordinary corn contains n per cent of protein, of which about 

 one half consists of the proteid zein. This nitrogenous substance 

 has been separated, purified, and investigated with very great care, 

 especially by Chittenden and Osborne (American Chemical Journal 

 (1891), jj, 453, 529; (1892), 14, 20). The percentage composition 

 represents the average of several closely agreeing analyses of what 

 was believed to be very pure zein. Based on the percentage of 

 sulfur, the molecular weight cannot be less than about 5000, and 

 the formula given above or some multiple of it must be approxi- 

 mately correct. 



Certainly the proteid molecule is exceedingly complex, and the 

 number of different proteids is very large. They all contain 

 nitrogen, usually about 16 per cent, and some of them contain 

 also sulfur and phosphorus. 



Sulfur. This is an essential element for all plants, but the amount 

 required for normal growth and full development is relatively very 

 small, even when compared with the small percentage present in 

 the earth's crust.' Most proteids (as zein, for example) contain 

 sulfur, but the percentage is usually very low. It is present, 

 however, in organic combination, and does not give the ordi- 

 nary tests for sulfates, the form in which it is usually taken from 

 the soil. 



Many of the simpler organic compounds of sulfur are well known, 

 and some can be made artificially. The oil of onions and garlic, 

 which gives to those plants their peculiar odor and taste, consists 



