W. E. BRENCIILF.Y AND A. D. HaLL 211 



until a later period than the others) remain constant during the filling 

 stage, indicates that these materials belong to the active cells which 

 are being filled, rather than to the cells which have been filled up and 

 put out of action. 



Finally ripening begins about six days before cutting, and the 

 characteristic feature is the rapid desiccation of the grain ; the actual 

 water falls as the remaining active cells fill up, the non-protein nitrogen 

 drops, and the precentage of nitrogen in the material still entering 

 increases, because the losses by respiration overtake the gain by 

 migration. The maximum weight of dry matter is reached a few 

 days before the grain appears to be ripe for cutting, because the intake 

 ceases, while respiration still continues. Cytologically this last stage of 

 ripening is marked by the progressive destruction of the nuclei in the 

 endosperm as they are squeezed into networks by the pressure of the 

 starch grains, but no sequence can be traced in the regions showing 

 such deformed nuclei, such as was observed by Brown and Escombe 

 in barley, which shows a progressive ' nuclear senescence ' with 

 ripening. 



Relation of the migration process to the nutrition of the whole 

 plant. Since the publication of Pierre's investigations {loc. cit.) it has 

 been generally held that the wheat plant ceases to draw nutriment from 

 the soil after a comparatively early date — the flowering period or a little 

 later. Assimilation, however, was considered to go on later, but to cease 

 in its turn before the migration into the grain had been completed ; 

 it has even been held that there is a return of nutrient materials to 

 the soil, an actual excretion of phosphoric acid, nitrogen, &c. in the 

 final stages. Such a complete cessation of nutrition and assimilation 

 must however be a matter of season and climate ; as long as any part 

 of the plant remains green assimilation will go on, water will be drawn 

 from the soil, and with the transpiration current nutrient materials will 

 enter the plant. In 1908 the straw belonging to each of the marked 

 ears was cut off close to the ground and analysed in order to trace the 

 relationship between migration and the nutrition of the whole plant. 

 The ratio between grain and straw in these selected shoots was deter- 

 mined and as before the unit yield at each date is represented by the 

 material contained in 1000 grains and also in the straw which was found 

 to be associated with 1000 grains at that period. 



Fig. 16 shows the dry matter curves for the whole plant and for the 

 grain ; from which it will be seen that the dry weight of the whole plant 

 increases up to within a week of cutting, i.e. the point when desiccation 



