CHAPTER XXV 

 Chemistry of Plant Growth 



328. Seeds. A seed is an embryo plant surrounded 

 by reserve food materials in the form of mineral matter 

 and nitrogenous and non-nitrogenous compounds. 



329. Ash of Seeds. The proportion of ash in seeds is 

 small compared with that in other parts of plants. For 

 example, the* wheat kernel contains 2 per cent, and 

 the straw 7 per cent.; corn contains 1.75 per cent, and 

 the stalks 7 per cent. While seeds contain comparatively 

 little ash, this ash is more concentrated in the essential 

 elements than that of the other parts of plants. In the 

 seeds are stored large amounts of phosphorus pentoxid, 

 magnesia and potash (ash elements which are of most im- 

 portance for the nutrition of the young plant), while in 

 the straw are found the largest amounts of the non- 

 essential mineral elements, as silicon, sodium and chlorin. 

 The per cent, of the various ash elements in cereals and 

 other seeds is given in Section 209. The amount of ash 

 in seeds is quite constant, more so than in the stems, 

 leaves or other parts of plants. In mature wheat, there 

 is rarely more than 2.10 per cent, or less than i. 80 per 

 cent. , while in the straw, the amount may range from 5 to 

 9 per cent. Constancy of composition is a characteristic 

 of the ash of seeds. 



330. Non-Nitrogenous Compounds of Seeds. Starch, 

 cellulose, and fat are usually the most abundant non- 

 nitrogenous compounds in seeds. Small amounts of 



