19 2o] JOXES— MAPLE SEEDS 141 



embryo fails to respond when placed in favorable germinative con- 

 ditions. The reason for this loss of vigor is not known. It may 

 be due to the increased respiration, using up the plastic substances 

 essential for the initiation of germination, or to the introduction 

 of some new factor inhibitory to growth. After-ripened seeds 

 placed at — 5 C. and kept saturated by packing in snow will retain 

 their initial vigor for a considerable time. 



Oxygen pressure 



most 



studied in detail. Seeds after-ripened in desiccators are under 

 considerably reduced oxygen pressure. The oxygen is soon used 

 up in respiration. Nevertheless, these seeds stored at a low 

 constant temperature will after-ripen quicker than seeds stored out 

 of doors with a good supply of oxygen, but subjected to fluctuating 

 temperatures. Seeds stored in open baskets, but kept saturated 

 at low constant temperatures, will after-ripen sooner than those 

 stored in desiccators, and the resulting seedlings appear to be more 



vigorous. 



peroxidase 



Eckerson (11) found an increase in oxidase and peroxidase 

 activity accompanying after-ripening in the haw. In the peach 

 Crocker and Harrington (6) found no increase in oxidase activity 

 m the after-ripening seeds when ordinary chromogens or the Bunzel 

 methods were used, but the pulp of the after-ripened seeds exposed 

 to air shows a more rapid oxidation of its own chromogens. In the 

 sugar maple there is a slight increase in peroxidase activity accom- 

 panying after-ripening, being more pronounced in the hypocotyl. 

 No oxidase could be detected in dormant or after-ripened seeds 

 when guaiaconic acid or benzidine was used as a chromogen. 



Catalase 



One of the most consistent phenomena accompanying the 

 after-ripening of this type of embryo is the increase in catalase 

 activity. This increase is continuous, increasing many fold during 

 the early stages of germination. Eckerson (ii) found that 

 catalase activity increased in the haw with after-ripening. In 



N 



