Oct, 21, 1918 Catalase and Oxidase Content of Seeds 153 



minating grain grasses. In other grasses that are markedly resistant 

 to germinating conditions the period is longer and the increase in ger- 

 minative capacity very marked {3, 21). Even in the grasses that ordi- 

 narily germinate readily, the dormancy may be deepened and the after- 

 ripening rendered slow and important by certain conditions during 

 ripening. This is true of ' 'rain barley" (36) (barley ripening during rainy 

 weather), and to a degree of "frosted grains" (grains frosted during the 

 early stages of ripening) (34, p. 436). So far as studied, the dormancy in 

 grass seeds seems to be imposed mainly by coat structures, and there is 

 no evidence of rise in vigor of the embryo with after-ripening, as there is 

 in peach and other seeds in which the embryos have a self-imposed dor- 

 mancy. It is also interesting to note that in the grasses there is no rise 

 but a very considerable fall in catalase activity with after-ripening, while, 

 as shown in a later section, there is a great rise in catalase activity with 

 after-ripening in seeds in which the embryos themselves determine the 

 dormancy. 



There is no evidence that the catalase of Johnson grass differs essen- 

 tially either in amount or time lability from that of Sudan grass, 

 although the seeds of the former are very refractory to germination 

 conditions, and the latter respond readily. 



In the seeds of Amaranthus retro flexus there is considerable variation 

 in the catalase activity of the several crops studied, but there is no 

 regular fall with age or even viabiHty of the seeds. The catalase of 

 this seed seems to be far more nearly time stable than is that of the 

 grasses studied. 



Crocker and Groves (17, 23) have offered considerable evidence for 

 the conception that age degeneration of seeds is due to a time-tempera- 

 ture denaturirg of certain colloids (probably proteins) of the embryo. 

 There also seems to be a time denaturing of the catalase of seeds, but 

 it does not parallel the time denaturing of the materials essential to 

 viability. The time lability of substances connected with viability 

 may be compared with the time lability of catalase. The former are 

 relatively time-stable in seeds of Johnson grass and Sudan grass (at 

 least for the early period of storage), while the latter is relatively time- 

 labile. In species of Amaranthus the former are relatively time-labile, 

 while the latter is nearly time-stable. 



Evidence given in other parts of the paper indicates that catalase 

 activity is more closely correlated with respiration intensity than it is 

 with viability; but the correlation with respiration is evidently not uni- 

 versal, for one can hardly conceive that seeds of Amaranthus retro flexus 

 that have died from age still maintain full respiratory vigor. 



The slower or lower percentage of germination shown in the 191 7 

 Johnson grass and two lots of the 191 7 Ainaranthus retro flexus seeds is 

 due to the unafter-ripened condition and not to low vitality. The seeds 

 of A. hlitoides and A. graecizans show a much lower catalase activity 



