170 BOTANICAL GAZETTE [march 



at lower temperatures (time of exposure not given) the speed of 

 germination fell with heating. Hohnel (17) in 1877 found that 

 most seeds with a moisture content below 3 per cent would endure 

 a temperature of no-125 C. for 15 minutes. In 1902 Dixon (13) 

 summarized the earlier work on high temperatures of seeds as 

 follows: "(a) imbibed protoplasm resists 30-40 C. more than the 

 optimum temperature; (b) dry protoplasm resists ioo° C. more than 

 the optimum temperature of the protoplasm of imbibed seeds 



?> 



time 



temperature 



time of germination 

 tat 30-60 per cent o 



j 



may be exposed to a temperature of 98 C. without losing their 

 ability to germinate, if first dried at 6o° C. for 24 hours and then 

 heated to 98 for 10 hours. 



The cause of the loss of viability in old seeds has been a matter 

 of considerable discussion and investigation. Duvel (14) states 

 that seeds retain their viability longest in conditions which permit 

 least respiration, implying that the food materials are exhausted. 

 Acton (i), by a careful analysis of old and new seeds, found that 

 there was but a slight difference in their food content. In the 

 course of these investigations he discovered that there was consider- 

 able diastatic and proteolytic enzyme action in new seeds, while in 

 old seeds there was none. He assumed, therefore, that the loss 

 of viability is related to the loss of enzyme activity. The investi- 

 gations of Thompson (31), Waugh (m), and others furnish some 



V 



evidence for this conclusion. They found that old seeds with a 

 low percentage of germination, when soaked in enzyme solution, 

 showed an increase in viability. Brocq-Rousseau and Gain 

 (8, 9, 10, 11) in their earlier work found that enzymes gradually 

 disappear with age. They tested 300 species of seeds and found 



sam 



century. 



enzymes in sam 



as old as 200 years. In some cases the retention of enzymes was 

 attributed to the hard coats of the seeds, and the loss of viability 

 was stated to be due to some cause other than degeneration of 

 enzymes. Aspit and Gain (3) found enzyme activity in seeds 





