RESPIRATION OF WHEAT 91 



produce a marked respiratory acceleration. In this respect 

 glutenous material* is important in that its degree of viscosity 

 is lowered as it takes up water ; this permits a more rapid 

 diffusion and hence a greater respiration. This is illustrated 

 in the fact that soft starchy varieties of wheat exhibit a higher 

 respiration intensity than hard vitreous wheats with the same 

 percentage of water. The embryo is the seat of enzyme 

 secretion ; shrivelled wheat, which contains less endosperm 

 and the same amount of embryo as compared with plump 

 wheat, shows a respiratory activity twice or thrice as much as 

 plump with the same water content, 14 per cent; with less 

 water than 1 4 per cent, there is little or no difference between 

 the two kinds of grain. The effect of respiration in bulked 

 grain is a rise in temperature ; this is cumulative and causes an 

 acceleration in respiration up to about 55 C., which temperature 

 also has the effect of stimulating diastatic activity and hence 

 rendering available more immediately respirable material. On 

 the other hand, the resulting accumulation of carbon dioxide 

 has a narcotic effect and reduces the rate of respiration. 



SALTS. The action of salts on the intensity of respiration 

 varies according to their chemical nature, their concentration 

 and their association with other salts ; thus salts of the heavy 

 metals are very toxic whilst those of the alkali metals and 

 alkaline earths accelerate or retard according to their concen- 

 tration and association. Nitrosomonas shows a maximum 

 respiration in N/2OO ammonia whilst a strength of N/io 

 depresses respiration in a marked degree. \ Similarly the 

 respiration of Bacillus subtilis is constant in the presence of 

 low concentrations of the chlorides of sodium, potassium and 

 calcium ; an increase in concentration leads to a reduction 

 in respiration. As compared with cultures lacking these salts, 

 the respiration intensity is increased by the presence of sodium 

 chloride, potassium chloride, calcium chloride or magnesium 

 chloride in concentrations of '2M, 'I5M, 'O5M, and 'C^M re- 

 spectively. In higher concentrations the rate of respiration 

 is decreased.} The use of mixtures of salts accelerate or retard 



Vol. L, p. 333- 



t Meyerhoi : " Pfluger's Archiv.," 1917, 166, 240. 



: Brooks : " Journ. Gen. Physiol.," 1919, 2, 5 ; 1920, 2, 331. 



