LIFE SPAN OF SEEDS 39 



Sherman ^" found that dormant imbibed Amaranthus retroflexiis seeds have 

 an initial rate of respiration which, if maintained, would exhaust all the 

 stored starch (47 per cent of the dry weight) within 160 days at 20° to 

 25° C (68° to 77° F). On this basis, even at 10° C (50° F), the stored 

 starch would last no more than a year. In spite of this, Deal's experiments 

 show that Amaranthus retroflexus seeds remain alive in the soil for 40 years. 

 Atwood ^^ found that dormant seeds of Avena fatua, which had lain dor- 

 mant in the germinator for a few days, showed great reduction in oxygen 

 consumption. 



Denny ^^ finds that gladiolus corms can be kept in moist soil in the 

 dormant fresh condition for much more than a year if, immediately after 

 digging, they are placed in soil at 20° to 27° C (68° to 80° F) and kept at 

 that temperature. In this condition they have very low respiration, using 

 up less than 20 per cent of their sugars and starches in a year. This leaves 

 out of consideration other stored foods, such as glucosides. When they 

 are removed from the soil the respiration intensity rises 5- to 30-fold or 

 more in a few hours, then gradually falls back to the original rate. The 

 curtailed respiration in the dormant corms -^ would make the life duration 

 in this condition perhaps five years, so far as food is concerned. Other 

 factors, however, limit the life under the conditions mentioned above to 

 two years or less. Barton ^°* finds that dormant seeds of Amaranthus 

 retroflexus in a germinator at 20° C (68° F) show a gradual fall in respira- 

 tion with lapse of time. After 125 days in the germinator the CO2 output 

 has fallen to about one-sixth the original rate. Evidently imbibed dor- 

 mant plant organs in nature have a means of conserving the food by cur- 

 tailing respiration. The mechanism of this curtailment is no doubt very 

 complex and the details of it are not known. The curtailment of respira- 

 tion must be enormous, however, in a case like Amaranthus seeds, in order 

 to conserve a year's food supply so that it cares for the needs of the embryo 

 at least for 40 years. Poor oxygen supply in compact soil may also lower 

 respiration. There is need for a detailed study of the course of change in 

 the respiratory intensity of such seeds as they lie in the soil, as well as the 

 mechanism by which the respiratory intensity is reduced. 



Ewart,^ BecquereV^ and others have assumed that long life span in 

 seeds is necessarily connected with hard-coatedness. The buried-seed work 

 of Beal and the U.S.D.A. brings to light the fact that many seeds with- 

 out hard coats have long life span in the soil, and it is probable that many 

 retain their vitality much longer in the soil in the imbibed condition than 

 in ordinary dry storage in the air. 



Table 7 was assembled by selecting seeds of species that show long life 

 span in the soil, as reported by Beal and the U.S.D.A., and that at the 

 same time appear Avith a number of records for life span in ordinary dry 

 storage in Ewart's assembled tables. In some cases Ewart's tables do not 

 show adequate records on the particular species of a genus with which 

 Beal and the U.S.D.A, worked, but do give many records for other species 



