64 CHANGES OF COMPOSITION [chap. 



grain during this period was far greater than would be 

 accounted for by what the plant had taken up meantime 

 from either the soil or the air. In fact, at the finish, 

 although only two-fifths of the whole dry matter of the 

 plant was collected in the grain, yet 80 per cent, of the 

 nitrogen and 70 per cent, of the phosphoric acid of the 

 whole plant had been transferred to it This, of course, 

 is only another example of the process which we have 

 already noted as taking place when the leaves died off 

 one by one — the valuable materials they contained were 

 constantly transferred to the still living and active parts 

 of the plant. In the same way, the seed is just that part 

 of the plant which has to carry on its life in the next 

 generation, and it is endowed with as much as possible 

 of the material that has been with difficulty accumulated 

 by the parent plant. 



During the formation of the grain itself, three stages 

 may be distinguished ; for about three weeks from the 

 time of flowering the main process that is going forward 

 is the formation of what later become the outer 

 envelopes of the grain, in a thick and fleshy form which 

 they lose afterwards. This " pericarp," as it is called, is 

 richer than the ultimate grain in nitrogen and ash, 

 though the ash does not contain so much phosphoric 

 acid. There is, of course, no sudden break which marks 

 the oncoming of the second stage, but towards the end 

 of the third week the formation of the pericarp has 

 ceased and the filling in of the endosperm begins to be 

 the main process going forward ; as this progresses, the 

 pericarp is denuded of the material already accumulated 

 there and becomes reduced to the series of tough, dry 

 membranes, with which we are familiar later as the chaff 

 and skin of the grain. The filling of the endosperm 

 continues for nearly three weeks, and the most notable 

 feature is that the material migrated by the plant from 



