152 



Journal of Agricultural Research 



Vol. XV, No. 3 



Figure 2 shows graphically the change in catalase activity and the 

 percentage of germination with aging in Johnson grass seeds. The 

 rather great irregularity in these curves is probably largely due to the 

 diversity of source and handling of the several crops. In general, how- 

 ever, the catalase curve is concave upward while the vitaUty curve is 

 convex. The rise in germination during the first year is due to after- 

 ripening and not to increased viability, for treatment of the new seeds 

 raised their germination to practically 100 per cent. It is interesting 

 to note the similarity of these curves to the catalase viability curves in 



heated seeds given on 

 p. 154. This similarity 

 strengthens the coagu- 

 lation conception of age 

 degeneration (p. 154). 



Catalase activity 

 might easily be used as 

 a method of estimating 

 the age of seeds. If such 

 were done, the following 

 precaution would be 

 necessary: The test 

 must be compared with 

 a crop of seeds of the 

 same variety and of 

 known age and like ma- 

 turity, to serve as a 

 standard. It could be 

 applied only to seeds 

 that have markedly 

 time-labile catalase. It 

 must be known that the 

 seeds have gone through 

 .... no drastic catalase-de- 



FiG. 2.— Graphs showing changes in viability and catalase activity in _ 



Johnson grass, caused by aging; Solid line= catalase; broken line= stfOyiUg COUdltlOU, SUCh 



viabiuty. as subjcctiou to high 



temperatures or repeated wetting and drying. Before one could apply 

 this method to any particular kind of seed he would have to know in 

 detail the behavior of its catalase, and the method would show its mam 

 value when applied in conjunction with viability tests. 



Practically all grass seeds go through a so-called after-ripening period 

 following harvest. Air-dry storage or even storage in a drier condition 

 seems to be a good, if not the best, condition for after-ripening. After- 

 ripening is marked by improvement in rate and percentage of germina- 

 tion. The period of after-ripening is transient and is accompanied by 

 only moderate improvement in germination in most of our readily ger- 



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