LIFE SPAN OF SEEDS 61 



in amino nitrogen, and (c) a decrease in digestibility. These changes were 

 rapid at first and had slowed down considerably after two years of storage. 

 They were also much more rapid at 24.5° C (76° F) than at -1° C (30° F) 

 and in open as against sealed storage. Even in the favorable storage con- 

 ditions the changes were easily measurable in two years. We do not know 

 to what extent these changes occurred in the living germ or scutellum, and 

 to what extent in the more inert endosperm and aleurone layer; but the 

 fact that the proteins of white flour showed very much greater changes 

 than those of the intact grains suggests that the storage proteins are in- 

 volved in these storage changes. The changes were thought to be due to 

 enzyme action and oxidation. The latter change may be greatly reduced 

 in intact grains by the low oxygen permeability of the dry grain or seed 

 coats. While stored foods are not used up to any great extent in dry 

 stored seeds, no doubt they are being slowly denatured. 



Ewart -^' p-i^^ offers the following explanation: "Longevity depends not 

 on the food materials or seed coats, but upon how long the inert proteid 

 molecules into which the living protoplasm disintegrates when drying, 

 retain the molecular grouping which permits of their recombination to 

 form the active protoplasmic molecule when the seed is moistened and 

 supplied ^nth oxygen." This explanation is not satisfactory because it is 

 highly speculative and not capable of experimental proof. 



Crocker and Groves ''^ h^ve suggested that the degeneration of seeds 

 in dry storage may be due to the gradual coagulation of proteins of the 

 embryo. They applied Buglia's time-temperature formula for coagulation 

 of proteins to the degeneration of wheat grains at various temperatures 

 and at two different moisture contents, and found that the calculated 

 longevities agreed well mth the determined longevities for high tempera- 

 tures. The calculated longevities for lower temperatures were, however, 

 many times as long as the life span of wheat grains in ordinary storage, 

 but, as we shall see later, controlled storage prolongs the life span of seeds 

 tremendously. This explanation has the fault of being very general. 

 There are many different kinds of proteins in an embryo, and this work 

 does not throw any light upon the particular proteins that coagulate with 

 time. Furthermore, it throws no light on the possibility of the degenera- 

 tion of some particular mechanism of the living cells. 



It is possible that in seeds in dry storage the greatly curtailed respira- 

 tion leads to the accumulation of intermediate products of respiration that 

 are toxic to the delicate mechanism of the cell nucleus. Stubbe ^** has 

 suggested this as one possible cause of the degeneration of seeds in storage 

 and of the increased mutation sho\\'n by old seeds. Schwemmle ^' offers 

 some experimental evidence of the accumulation of inhibiting or toxic 

 substances in seeds as they age. In certain hybrids of Oenothera herteriana 

 the seeds germinated more slowly as they became older, and from the old 

 seeds he could extract substances that greatly inhibited the germination 

 of fresh seeds that showed prompt and complete germination in absence 



