CHEMICAL COMPOSITION OF PLANTS 



37 



In starchy seeds, on the contrary, there is usually very little 

 fat, as may be seen from these figures : 



In his agricultural activity, man cultivates primarily plants 

 with starchy seeds. He obtains these from cereals, which form 

 the major part of his diet. In general, however, oily seeds pre- 

 dominate in nature, being produced by about 90 per cent of all 

 plants. As they contain less oxygen and have a high energy 

 value, about which details will be given later, oils form more 

 concentrated reserves of nutritive substances than carbohydrates. 



Protein compounds always form a smaller part of a seed's 

 reserves, rarely reaching 25 per cent of its total weight. Oily 

 seeds usually contain a larger percentage of proteins than starchy 

 seeds. Hemp seeds contain 18 per cent of proteins; flax, 23 per 

 cent; poppy, 19 per cent; almond, 22 per cent; and sunflower 

 seeds, up to 30 per cent: whereas, in wheat, there is but 12 per 

 cent; in buckwheat, 10 per cent; in corn, 10 per cent; and in 

 rice, 7 per cent. The starchy seeds of leguminous plants, how- 

 ever, are rich in proteins, very much like the oil-containing seeds. 

 Thus, peas contain 29 per cent protein; kidney beans, 23 per 

 cent; lupines, 40 per cent; and soybeans as much as 44 per cent. 

 This high protein content of leguminous seeds is undoubtedly 

 connected with the ability of these plants to fix atmospheric 

 nitrogen owing to the activity of the tubercle bacteria (see Art. 

 53). Having at their disposal during the course of their lives 

 an unlimited supply of nitrogen, leguminous plants supply their 

 progeny with a liberal amount of nitrogenous substances. 



10. The Chief Representatives of Carbohydrates in Seeds and 

 Other Parts of the Plant. — According to Kiesel's analysis, stated 

 above, carbohydrates make up about 25 per cent of the total 

 dry weight of protoplasm of slime molds. But in the body of 



