iqiq] current literature 309 



however, and sterile florets show very low activity, especially after a year of 

 dry storage. It is suggested that in these cases, where presumably dead 

 tissues give catalase reaction, the activity is a residuum of previous physiologi- 

 cal activity. In the grasses, catalase activity decreases continuously from the 

 time the seeds are harvested. This decrease, however, is in no way connected 

 with loss of vitality. Even when the activity has fallen to one-half or one-third 

 of the fresh harvested material, there may still be practically complete vitaHty, 

 and but slight loss in vigor. The investigation indicates that under certain 

 conditions catalase activity might be used to estimate the age of seeds. It 

 would only be necessary to know the normal rate of activity decrease, to be 

 sure that no accidental destruction of catalase activity had occurred, and to 

 use proper controls of materials of known age and of equal maturity with the 

 seed to be tested. 



When dormancy occurs in grasses it is usually caused by seed coat char- 

 acters. Thorough drying at about 20° C. is the best after-ripening condition, 

 but during drying catalase activity is falling rapidly. Seeds of Aniaranthus 

 retroflexus also have a dry after-ripening period, but in these the catalase is 

 time-stable, and very little decrease in catalase activity occurs during drying. 

 In contrast to these there are other seeds, as peach, linden, and hawthorn, where 

 dormancy is due to embryo conditions, in which after-ripening, which depends 

 mostly on cool temperature and moisture, is accompanied by a rapid increase 

 in catalase activity and other fundamental time-requiring chemical changes. 

 Such chemical changes, aside from catalase decrease, do not occur in the grasses. 

 Heating air^dry seeds finally reduces both vitality and catalase activity, but 

 the denaturing of the catalase and the proteins upon which viability depends 

 does not run parallel. Catalase decrease commences at once; but viability 

 may increase temporarily, and then decrease to zero before the catalase is 

 destroyed. In other cases viability is soon lost, but catalase activity remains 

 high, as in Amaranthus. 



Seeds of Johnson grass kept in a germinator at room temperature undergo 

 secondary dormancy and lose their catalase activity rapidly. The respiratory 

 activity falls correspondingly. If these conditions are repeated in seeds buried 

 in the soil, they may have an important bearing on the longevity of buried seeds. 

 If death depended upon destruction of food supply by respiration, decreased 

 respiration would provide longevity. When seeds of Johnson grass germinate, 

 there is a very rapid increase again in the catalase activity. At every point 

 it seems that catalase activity and respiration intensity run parallel. Some 

 tests of oxidase activity were made with the same seeds, and it is shown 

 that oxidase activity decreases with age. Little relation was found between 

 oxidase and after-ripening changes in grasses or peach seeds, and oxidase 

 activity showed no increase in germination, but in those non-living parts, bracts 

 and scales, where catalase activity was low, oxidase activity was relatively 

 high. The oxidase of Johnson grass and the Tunis grass-sorghum hybrid is only 

 slightly sensitive to mercuric chloride poisoning. 



