380 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



plant. The reserve carbohydrates undergo changes similar to 

 the fat. In some seeds, as in barley, ferments are formed which 

 change starch into sugar. 



The change in composition of seeds on sprouting may be 

 studied by allowing a weighed quantity of seed to sprout in the 

 dark, and determining the constituents of the original seed, and 

 of the sprouted seed. The sprouting must take place in the 

 dark, since when light is present carbon dioxide is assimilated 

 and masks the change. 



Composition of Plants at Different States of Growth . Plants do 

 not have the same composition at different stages of growth. The 

 plant increases in weight up to maturity. In the earlier part of 

 the life of the plant, nitrogenous material is taken up more 

 rapidly. Before the formation of fruit, the reserve material pro- 

 duced is stored up in leaves, stem, roots, or tubers. At the time 

 of fruiting, this reserve passes into the seed. During the later 

 stages of plant growth, lignification of the tissues takes place. 

 That is to say, the cellular material becomes penetrated with 

 lignin and the stems, etc., become more woody and difficult to 

 digest. 



The composition of plants at different stages of growth mav 

 be studied in two ways. 



The first method consists in selecting and analyzing averagt 

 specimens of the plant at the desired periods of growth. This 

 method of experiment shows the change in the individual plant. 



The second method consists in harvesting definite areas of the 

 same field when the field has reached the average condition de- 

 sired and subjecting samples to analysis. This method represents 

 the production of the field at different stages of growth. The 

 plants harvested are not all in the same condition of growth. 

 This method is better suited for small plants and grasses than the 

 first method. Both methods are open to error, as there may be 

 differences in the soil or in the individual development of differ- 

 ent plants. 



The general results of these experiments are as follows : 



The water in the green plant decreases with the age of the 



