IV.] QUALITY IN WHEAT 65 



day to day possesses an almost constant composition 

 throughout the process, containing the same proportion 

 of carbohydrates, nitrogen compounds, phosphoric acid, 

 etc. It is a mistake to suppose that the proteins which 

 form the gluten are filled in first, and that starch only 

 enters towards the later stages of filling and ripening. 

 But though any particular lot of wheat does in this way 

 pass on a constant mixture of materials from its reserves 

 to the grain, there will be certain differences in the type 

 when different varieties or the same variety grown in 

 different climates or soils are compared. Each plant 

 in a given field of wheat possesses, as it were, a mould 

 wherewith to fashion the material it passes on to its 

 grain, and the form of the mould is determined by the 

 variety and the environment — soil, climate, season, etc. 

 Wheats grown in certain climates, such as those prevail- 

 ing in Kansas, Manitoba, or Hungary, are specially 

 nitrogenous (glutenous or " strong " wheats), but this is 

 not due to the hot dry climate shutting down the 

 migration process prematurely before the later stages 

 are reached, when starch only enters the grain, but 

 to the fact that the environment — climate and soil, 

 together with the varieties appropriate to such con- 

 ditions — causes the wheat to make that which we 

 have called its mould on a nitrogenous type. It 

 should, however, be noted that though variations 

 due to environment do occur, the composition of the 

 grain of wheat is singularly constant. It has already 

 been explained how all plants react against variations 

 in the composition of the soil and select the particular 

 constituents appropriate to their nutrition ; so, similarly, 

 when the migration process begins, the plant again 

 effects a re-sorting of the material accumulated, and only 

 passes on its usual constituents to the grain. Thus the 

 straw will always vary much more in composition from 



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