COMPOSITION EST SUCCESSIVE STAGES. 213 



by Arendt that of the stem the upper portion was richest in 

 asli throughout the whole period of growth. Of the leaves, 

 on the contrary, the lower contained most fixed matters. 

 In the ear there occurred a continual decrease from its 

 first appearance to its maturity, while in the stem and 

 leaves there was, in general, a progressive increase towards 

 the time of ripening. The greatest percentage, (10.5° |„,) 

 was found in the ripe leaves ; the smallest, (0.78° |„,) in the 

 ripe lower straw. 



Far more interesting and instnictive than the relative 

 proportions are 



B — The absolute quantities of the iugredients found 

 in the plant at the conclusion of the several periods of 

 growth • — These absolute quantities, as found by Arendt, 

 in a given number of carefully selected and vigorous 

 - plants, do not accord with those obtained by Bretschnei- 

 der from a given area of ground, nor could it be expected 

 that they should, because it is next to impossible to cause 

 the same amount of vegetation to develope on a number 

 of distinct plots. 



Though the results of Bretschneider more nearly rep- 

 resent the crop as obtained in farming, those of Arendt give 

 a truer idea of the plant when situated in the best possible 

 conditions, and attaining a uniformly high development. 

 We shall not attempt to compare the two sets of observa- 

 tions, since, strictly speaking, in most points they do not 

 admit of comparison. 



Prom a knowledge of the absolute quantities of the sub- 

 stances contained in the plant at the ends of several periods, 

 we may at once estimate the rate of growth, i. e., the rapid- 

 ity with which the constituents of the plant are either taken 

 up or organized. 



The accompanying table, which gives in alternate col- 

 umns the total weights of 1,000 plants at the end of the 

 several periods, and, (by subtracting the first from the 



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