1 56 Journal of Agricultural Research voi. xv, No. 3 



Table XX. — Effect of heating i-year-old Johnson grass seeds for i hour at 81° C. upon 



rate of germination 



It is evident that moderate heating of Johnson .grass seeds reduces 

 both their catalase activity and respiratory intensity, while it increases 

 the germinative capacity. It seems to lead to a more economic use of 

 food — that is, a lower percentage of it is respired and a larger percentage 

 is available for building new organs. A number of substances are 

 capable of modifying the economic coefficient of plants (25, p. 249-230). 

 This may be part of the benefit claimed for heating seeds, while more 

 rapid germination is also a part. It would be interesting to "know how 

 long this effect persists in the seedlings from heated seeds. The fact 

 that the ratio is less than i in the third period (Table XIX) does not 

 indicate that the effect is lost. This low ratio is probably due to the 

 more advanced stages in the germination of the heated seeds, for 

 Rischawi (jj, p. 233) has shown that respiratory intensity increases 

 as germination progresses in the grasses. 



Table XVIII shows that seeds of Amaranthus retroflexus lose their 

 viability rapidly, while the catalase falls relatively slowly with heating 

 at 81° C. The vitality is reduced to 25 per cent after 0.5 hour and to 

 nil after 4 hours of heating, while the catalase activity is still about 

 60 per cent of its original intensity even after 48 hours' heating at 81° C. 

 In seeds of A. retroflexus the catalase is comparatively heat-stable, while 

 the substances essential to viability are comparatively heat-labile. 



The findings of the last two sections may be summarized by saying 

 that the catalase in air-dry seeds of Amaranthus spp. is comparatively 

 heat- and time-stable, while the substances connected with viability are 

 comparatively heat- and time-labile. In the main, exactly the reverse 

 is true for Johnson grass. 



EFFECT OF RETENTION IN A GERMINATOR 



The catalase activity of Johnson grass is greatly reduced by retention 

 in a germinator. This effect is shown in Table XXI. The seeds in a 

 germinator at 20° C. for one year show from one-third to one-sixth the 

 catalase activity of those dry-stored for the same period. This fall in 

 catalase activity evidently begins soon after the seeds are placed in the 

 germinator, for the seeds in the germinator for one month at 20° C. have 

 less than one-half the catalase activity of the same seeds dry-stored. 

 The fall in catalase activity is also much slower at 7° C. 



