Mar. is, lyib Respuation of Stored Wheat 687 



quotient found for one period of their studies, when conditions for 

 accurate measurement were at an optimum, was 2.6. This is so nearly 

 the theoretical for the combustion of carbohydrates as to indicate that 

 little else was involved. As pointed out by Dr. Milner in a private 

 communication, the thermal quotient when fat is burned is 3.4, while 

 that when protein is burned is 2.9. 



Hasselbring and Hawkins (1913) found no general correlation between 

 the total sugar content of the sweet potato and its respiratory activity. 

 Cane sugar is relatively stable and does not appear to be used in the 

 process of respiration. A simultaneous decrease in the reducing sugars 

 and the respiratory activity was observed. The reducing sugars are, 

 in their opinion, the immediate source of respiration material. 



That the fat or ether extract of the wheat embryo is not the principal 

 substrate upon which the respiratory enzyms act, and that it is not 

 burned or destroyed during germination is indicated by the experiments 

 of Le Clerc and Breazeale (1911, p. 12). Their data show that there w^as 

 more fat in the total plant (seed residues plus axes) at practically all 

 stages of germination than there was in the original seeds. Accordingly 

 little energy could have been derived from the oxidation of the fats; on 

 the contrary, energy derived from some other source must have been 

 utilized in the synthesis of the additional fat produced in the seedling. 

 All available evidence therefore seems to indicate that the heat of respira- 

 tion is produced by the oxidation of reducing sugars. 



SEAT OF RESPIRATION IN THE WHEAT KERNEL 



There are a number of reasons for believing that the germ or embryo 

 of the wheat kernel is the location of the larger part of the biological 

 oxidation that occurs incidental to respiration. The embryo is, in a 

 general w^ay, decidedly richer in enzyms than is the endosperm or any 

 other kernel structure. Brown and Morris {i8go) consider that the 

 endosperm of the ripened kernel is no longer a vital tissue. The secretion 

 of diastase and other enzyms is assigned to the scutellum, an organ of the 

 embryo. Maim and Harlan (1915) concluded that in germinating 

 barley the conversion of the endosperm is effected by enzyms secreted 

 by the epithelial layer of the scutellum. 



Karchevski (1903) found the energy of carbon-dioxid respiration 

 to be 12 times as great in the wheat embryos as in the seeds themselves. 

 Burlakow {1898) states that the respiratory activity of the germ is 20 

 times greater than is that of the endosperm. Wender {^1905) called 

 attention to the pronounced catalase activity of the germ structures, 

 as contrasted with mill products derived almost exclusively from the 

 endosperm. This has also been observed in an unpublished study of 

 catalases which was made in this laboratory. This fact is more signifi- 

 cant, in view of Appleman's {1915) discovery that catalase activity in 

 potato juice shows a striking correlation with respiratory activity in the 



