154 



Journal of Agricultural Research 



Vol. XV. No. 3 



than the seeds of A. retroflexus. They also show slower germination. 

 It is not known whether the low catalase activity in these two species 

 is due to a relatively low percentage of embryo material (the main seat 

 of catalase) in the seeds, to some other specific difference in these seeds, 

 or to lower vigor. The slow germination, however, may represent an 

 unafter-ripened or dormant condition rather than low embryo vigor. 



Seeds of Amaranihus retroflexus after- ripen during the first three or 

 four months in dry storage. There is no evidence of embryo dormancy 

 here. After-ripening is not marked by an increase in catalase activity. 

 In this respect it resembles Johnson grass, but, unlike seeds of Johnson 

 grass, there is no fall in catalase activity with age. 



I' 



bi/O 





fiu/f/pr/ay o^ r/fe'/iia^7yi'\K://i///oe/r>s 



Fig. 3. — Graphs showing changes m viability and catalase activity in Johnson grass caused by heating 

 air-dry seeds at 81° C. for various lengths of time: Solid line= catalase; broken liae= viability. 



EFFECT OP HEATING AIR-DRY SEEDS tTPON THEIR VITALITY, CATALASE ACTIVITY, AND 



RESPIRATION 



Heating air-dry seeds causes a fall in their vitality as well as in their 

 catalase activity, but the denaturing of the substances connected with 

 viability and of the catalase do not parallel each other (Table XVIII). 



Heating Johnson grass to 8i° C. for half an hour to two hours reduces 

 the catalase activity by a large percentage and improves the germina- 

 tion. Longer heating ( four hours at 8i° C.) causes considerable addi- 

 tional reduction in the catalase activity and a very decided fall in ger- 

 mination. Still longer heating (17 hours, at 81° C.) reduces the catalase 

 to from 10 to 16 per cent of its original value and kills all the seeds. 

 Heating to 100° C. for five hours kills all the seeds and destroys all 

 their catalase. In the early stages of heat degeneration, as in time 

 degeneration, the catalase falls faster than the viability; but some 

 catalase activity persists after the seeds are all killed. The relative 

 rate of degeneration of catalase and vitality with heating is shown in 

 figure 3. 



