Oct. 21, 1918 



Catalase and Oxidase Content of Seeds 



157 



Table XXI. — Effect of retention in a germinator on catalase activity of seeds of Johnson 



grass 



This fall in catalase is accompanied by a fall in respiratory intensity. 

 Table XXII shows the rate of respiration of two samples of the same 

 collection of Johnson grass seeds, one stored dry and the other kept in a 

 germinator at 20° C. for one year. 



The gradual rise in the respiratory intensity of dry-stored seeds is due 

 to the initiation of germination. At the close of the third period several 

 had germinated in this lot, while none had germinated in the dormant lot. 



Table XXII. — Effect of retention in a germinator on the respiratory intensity of Johnson 



grass seeds 



[Intensity in milligrams of carbon dioxid per 10 grams, dry weight, per 24 hours at 20° C] 



Treatment of seeds. 



Respiratory intensity. 



First 

 period. 



Second 

 period. 



Third 

 period. 



I year in germinator at 20^^ 

 I year, stored dry 



3-6 

 9-5 



3-4 

 10. 6 



3-1 

 12. 9 



When freshly harvested Johnson grass seeds are put into a germinator 

 at 20° C, they become more dormant. The senior writer (75, p. iio-iiy) 

 has called this "secondary dormancy" and has mentioned that unfavor- 

 able germination conditions produce this in many seeds. If this deepened 

 dormancy is generally accompanied by lowered respiration, it may have 

 an important bearing upon the duration of dormancy of some seeds in 

 nature. It is conceivable that imbibed dormant seeds in the ground may 

 finally exhaust their stored foods by respiration and thus set a limit upon 

 their longevity. Leaching may also play a part. 



Reduction of the respiration, as in Johnson grass, will lengthen the 

 period necessary for exhausting stored foods. If 75 per cent of the weight 

 of the seed can be respired before death occurs, secondarily dormant 

 Johnson grass seeds could lie in a germinator for 9.8 years at 20° C. 

 before death would occur from exhaustion of stored foods. The period 

 at 10° C. would likely be 2 to 3 times 9.8 years, in accord with the tempera- 

 ture quotient for respiration (26, p. 153-154) . Without such a reduction in 



