474 Messrs. A. D. Hall and C. G. T. Morison. [Dec. 22, 



The further question of the intimate mechanism by which the silica acts 

 within the plant, and the nature of the chemical changes into which it enters 

 to bring about the observed effects, cannot yet be raised. In the first place 

 little is known of how the phosphoric acid itself acts ; it is evident that it 

 induces seed-formation and hastens maturity, but in what way it takes part 

 in the cell processes is still doubtful. Some of the data accumulated in the 

 present investigation may profitably bear discussion in this connection — 

 it is evident, for example, that there is little or no interdependence between 

 the phosphoric acid and the assimilation or migration of nitrogen, as has often 

 been suggested. Again, the results would seem to indicate that a distinction 

 must be drawn between physiological maturity and ripeness. The grains 

 of a phosphoric acid starved Plot like No. 1 go through a ripening process, 

 but they never approach to the composition, or even attain the appearance, 

 of the truly mature grain on more normal Plots like 2 and 4. The grain 

 from Plots 1 and 3, though ripe, has still many of the characters of immature 

 grain. If the progress of the grain be judged by such factors as the per- 

 centage of nitrogen or the ratio of phosphoric acid to nitrogen, the grain 

 early in its formation settles down to a standard composition correlated 

 with the original supply of nutriment, and after this point has been reached 

 it does not change its gross composition, though it is continually increasing 

 in size and weight. For example, the grain of Plot . 1, with its high 

 percentage of nitrogen and low ratio of phosphoric acid to nitrogen, which 

 might be taken as indicative of its generally immature character, shows no 

 tendency as its grows and ripens to approximate in composition to the 

 thoroughly mature grain of Plot 2. The later stages of ripening are without 

 doubt attended by changes in the nature of both the carbohydrate and the 

 proteid contents of the grain, which however are not apparent in the 

 elementary analysis of the grain. 



Conclusions, 



The following general conclusions have been reached in the course of this 

 investigation : — 



(1) Silica, though not an essential constituent of plant food, does play a 

 part in the nutrition of cereal plants, like barley, which contain normally 

 a considerable proportion of silica in their ash. 



(2) The effect of a free supply of soluble silica manifests itself in an 

 increased and earlier formation of grain, and is thus similar to the effect of 

 phosphoric acid. 



(3) The silica acts by causing an increased assimilation of phosphoric 



