Mar. i8. 1918 Respiratiou of Stored Wheat 709 



CONCLUSIONS 



(i) Deductions from these investigations support the findings of 

 earlier investigators that spontaneous heating in damp grain is occa- 

 sioned by the biological oxidation of dextrose and similar sugars, chiefly 

 in the germ or embryo of the kernel. 



(2) Moisture is one of the determining factors in respiration. It 

 establishes the comparative rate of diffusion between the several kernel 

 structures. Any gain in the moisture content of the kernel accord- 

 ingly increases the rate of diffusion and, simultaneously, the rate of 

 respiration. The increase is gradual and fairly uniform until the mois- 

 ture exceeds 14.5 per cent, in the case of plump spring wheat, when it 

 is markedly accelerated. 



(3) Density of the wheat Kernel generally parallels the gluten con- 

 tent. Gluten possesses the property of imbibing more water than starch, 

 and thus varying percentages of gluten result in varying degrees of 

 viscosity at the same moisture content. The relative viscosity affects 

 the rate of diffusion and this in turn directly affects the rate of respira- 

 tion. The soft, starchy wheats thus respire more rapidly than hard, 

 vitreous wheats containing the same percentage of moisture. 



(4) Plumpness of the wheat kernel affects the rate of respiration, as 

 shown by contrasting plump and shriveled grain. The shriveled wheat 

 respired two to three times as much as did the plump wheat at moisture 

 contents above 14 per cent. At percentages of moisture below 14 per 

 cent the difference is not very marked. The high acceleration of respira- 

 tion in shriveled wheat containing more than 14 per cent of moisture 

 is attributed to the higher ratio of germ to endosperm and hence the 

 larger percentage of enzym to substrate as compared with plump wheat. 



(5) The period of dampness — that is, the length of time the excess 

 moisture has been present in the wheat — bears a relation to the rate of 

 respiration. This is shown by comparing the respiration of freshly 

 dampened wheat with that of naturally damp grain and with grain 

 that had been dampened and stored for varying lengths of time. The 

 curve of respiration diverges from that of freshly dampened wheat when 

 the moisture content exceeds 12 per cent, and this divergence is more 

 marked after 13 per cent of moisture is reached. In the case of wheat 

 dampened and stored, the quantity of carbon dioxid respired varies 

 directly with the number of days the wheat remained in storage. The 

 temperature at which the grain is stored affects the rate of diastatic 

 action, thus increasing the quantity of substrate available to the respira- 

 tory enzyms. This is indicated by the greater rate of respiration of 

 wheat stored at room temperature than that stored at the outdoor 

 temperature during the winter months. 



(6) Unsoundness of wheat caused by the freezing of the unripe plant 

 results in higher respiratory activity in the threshed grain. This was 



