28O LECTURE XIII. 



afforded by seeds. In a series of experiments made upon the 

 seeds of a great number of plants (88 species) Haberlandt 

 found that the dry seeds were not in any case injured by 

 being exposed for forty-eight hours to a temperature of 77 C., 

 and that in some cases the seeds survived an exposure of the 

 same duration to a temperature of 100 C. He found, indeed, 

 that previous warming, if not excessive, was beneficial to the 

 seeds inasmuch as it shortened the period of germination. 



Thus, seeds warmed for 48 hours at temperatures of 

 37-5 C, 56 C, 75 C., 87-5 C, 



germinated in 



5-45, 5-2, 5-2, 5-03 days. 



Again, von Hohnel found that most seeds, provided that they 

 are quite dry, survive an exposure of one hour to a tempera- 

 ture of 1 10 C. He considers that the maximum-temperature 

 which dry seeds can bear for at least a quarter of an hour 

 without being killed, lies between 110 and 125 C. 



When seeds are exposed to a moist heat, or when they are 

 heated in water, they are killed at lower temperatures than 

 those mentioned above, and in a shorter time. Edwards and 

 Colin observed that an exposure of fifteen minutes to watery 

 vapour at 62 C. sufficed to kill more than half the number of 

 the seeds (of Leguminous and Cereal plants) experimented 

 with, and an exposure of the same duration to watery vapour 

 at 72 C. killed them all. Just found that an exposure of four 

 days duration to watery vapour at 40 C. was injurious to Oat- 

 and Barley-seeds ; that an exposure for 24 hours at a tempera- 

 ture of 50 C. was more injurious than the exposure for four 

 days at 40 C. : that exposure for 24 hours at a temperature 

 of 60 C. was fatal. With regard to the effect of heating seeds 

 in water, it must be borne in mind that a prolonged soaking in 

 water at ordinary temperatures is in itself prejudicial. The 

 prejudicial effect is remarkably increased as the temperature 

 of the water is raised. Edwards and Colin found that if 

 seeds are kept for a long time in water at a temperature 

 of 35 C. they are killed. This observation has been confirmed 

 and extended by Haberlandt and by Just. 



