Mar. i8, 1918 



Respiration of Stored Wheat 



691 



running from March 2 to March 29, 191 1, the following temperature 

 changes were observed in cars held on track at Baltimore, Maryland: 



In a similar experiment, running from May 11, 191 1, to June i and 3, 

 191 1, corn containing 16.9 per cent of moisture or more was heating 

 when unloaded, while that which contained 13.9 per cent of moisture 

 was still cool. The extent of heating bore a fairly definite relation to 

 the shrinkage or loss in weight of the grain. 



Bailey (1917a) reported to the Second Interstate Cereal Conference in 

 1916 the results of storage experiments with wheat at Duluth, Minn. 

 In the cool climate of that city it was found that wheat containing 15.5 

 per cent of moisture when put in a bin in the fall kept 333 days before 

 it developed a sufficiently high temperature to necessitate turning it, 

 while wheat containing 16.5 per cent of moisture was actively heating 

 in 49 days. 



The exact reason for an accelerated respiration with an increased 

 moisture content had not been adequately explained. In the discussion 

 referred to in the paper mentioned in the preceding paragraph an hy- 

 pothesis was advanced to account for this relation. Moisture in grain 

 may, in the light of recent discoveries in the field of physical chemistry, 

 be assumed to exist as imbibed water in loose combination with the 

 organic colloids. The organic colloids which form the principal con- 

 stituents of the wheat kernel have the property of imbibing considerable 

 quantities of water and forming elastic gels. The gel swells as the water ^ 

 is increased, although the total volume of the dry colloid plus the added 

 water is diminished. The water-imbibing capacity of the several colloids 

 varies widely, starch having an imbibing capacity materially lower than 

 that of wheat gluten. There is no fixed amount which a given dry 

 colloid will imbibe; thus, gels of varying viscosity can be produced, 

 depending upon the proportion of water present, and other variables, 

 such as temperature, mineral salts, and other substances. The rate of 

 diffusion in a gel varies with the viscosity, as pointed out by Plimmer ■ 

 (1975, p. 386). In dilute gels diffusion takes place as in water, while in 

 strong gels the rate is slower. It is probable that in very dry grain the 

 imbibed water is not sufficient to produce a gel in the endosperm struc- 

 tures. The colloidal material there located accordingly does not have a 



