158 Journal of Agricultural Research voi. xv, no. 3 



respiratory intensity the possible longevity would be a little more than 

 one-third as great, figured on the initial rate in the active seeds. Even 

 if the longevity of imbibed seeds in the soil be dependent upon some 

 contingent other than exhaustion of stored food, this reduction in 

 respiration is of significance. It will leave more stored material for build- 

 ing purposes in case germination does occur after a considerable period 

 in the soil. 



Atwood (j) observed that unafter-ripened seeds of Avena fatua become 

 more dormant after they have been in a germinator for a few days. The 

 power of the seeds to absorb oxygen falls with the deepened dormancy. 

 This may be parallel to the reduced respiration just discussed for Johnson 

 grass. There is also the possibility, however, that oxygen absorption in 

 the wild oats is limited by permeability characters and not by respiratory 

 capacity. There is need of following the changes in catalase activity as 

 well as carbon-dioxid production during the acquiring of deeper dormancy 

 in this seed as well as many others. 



It is quite within the range of possibility that longevity of imbibed 

 seeds in the soil is commonly limited by the exhaustion of stored foods 

 by respiration. Seeds of Amaranthus retroflexus retain their viability in 

 the soil for at least 30 years {18) and those of Brassica nigra fof many 

 years (2S). Both absorb a considerable percentage of water. The 

 same is probably true of many other seeds. In such seeds respiration 

 must be at a very low intensity to avoid death from food exhaustion. 



When the air-dry seeds (carpel removed) of the peach are placed in 

 a germinator the catalase activity rises continuously for more than 30 

 days and probably for more than 54 days, as shown by Table XXIII. 

 The rate of rise in catalase activity is very much greater at 7° C. than 

 at 20° or 25°, and it is somewhat greater at 20° than at 25°. The 

 temperature 5° has been shown to be very nearly the optimum for 

 after- ripening of the embryo of Crataegus spp., and it is an excellent 

 temperature, if not the optimum, for the after-ripening of the peach 

 embryo as well as other dormant embryos. The temperature 7° proved 

 very favorable for the after- ripening of the peach, as after 54 days 

 many of the seeds showed s^gns of germination, and 10 days later all 

 had germinated, while all those in the germinator at 20° and 25° were 

 dormant, except for the small percentage that germinated the first 

 few days, as always occurs when carpel-free seeds are put into a germi- 

 nator at 20° or 25°. These produce only stunted seedlings. 



It would be of interest to know whether rise in respiratory capacity 

 accompanies the very marked rise in catalase activity during the after- 

 ripening of peach seeds. Greatly increased vigor of the seedlings result- 

 ing from after-ripened seeds as well as the rather general parallel found 

 between catalase activity and respiration would suggest increased 

 respiratory capacity. 



