IV.] THE FILLING OF THE GRAIN 63 



as the wheat comes into flower, these processes begin to 

 slow down : in particular, the feeding of the plant upon 

 the soil becomes less. This may be traced in the 

 diagram. Fig. 15, which shows the amounts of dry 

 matter, nitrogen, and phosphoric acid contained in the 

 whole plant and in the grain separately, from the time 

 when the grain could first be separated — about a 

 fortnight after flowering — up to the time of harvest. The 

 curves show that at the starting-point the plant had 

 reached about 90 per cent, of its ultimate dry weight, 

 but that it had acquired only about 75 per cent, of the 

 nitrogen and less than 70 per cent, of the phosphoric 

 acid that were finally present in the plant. It should, 

 however, be noted that these figures take no account of 

 the root, which doubtless itself contained some of the 

 nitrogen and phosphoric acid that later found their way 

 into the above-ground parts of the plant. The earlier 

 experiments of Pierre, conducted in the hotter and drier 

 climate of France, would indicate that the wheat plant 

 ceases entirely to take nutriment from the ground at a 

 much earlier date — soon after flowering ; whereas in the 

 experiments quoted the processes of nutrition never 

 stopped until the whole plant was ripening ofl" for 

 harvest. Assimilation is also shown to be going on as 

 long as the plant possesses any green leaf tissue ; during 

 the last fortnight or so before cutting, the dry weight 

 did not increase at all ; in fact, it decreased because the 

 burning-up of carbohydrate by respiration continued to 

 go on and towards the end caused losses which out- 

 weighed the diminishing gains by assimilation. From the 

 time of the formation of the grain, the most important 

 process going forward was the migration into the seed of 

 the material that has previously been stored in the 

 stem. It will be seen that the gain of dry matter, and 

 particularly of nitrogen and phosphoric acid, by the 



