2/2 LECTURE XIII. 



The seeds of the following plants germinated at the end of the four 

 months at a temperature of 16 C. : 



Out of 21 5 Rye seeds ... 4 germinated. 



205 Hemp ... 76 



205 Mustard ... 2 



280 Lucerne ... 3 



452 White Clover ... 23 



The seeds of the following did not germinate at this temperature : 



Wheat, Barley, Oat, Rye-grass, Buckwheat, Beet, Gold-of-Pleasure, 

 Rape, Flax, Poppy, Vetch, Lentil, Pea. 



It has been found, in the second place, that exposure to a 

 very low temperature for a short time is not necessarily fatal, 

 and that the injury which a plant or any part of a plant 

 sustains depends very much upon the proportion of water 

 which it contains. The relation between the injurious effect 

 of frost and the proportion of water in the cells exposed to 

 it has been long known : it was definitely stated by A. P. de 

 Candolle so long ago as 1832, but the first experimental de- 

 termination of it appears to have been made by Goppert in 

 1830. He exposed seeds, some of which were dry, whereas 

 others had been previously soaked in water, to a temperature 

 of from 25 C. to -40 C., and he found that only the 

 moistened seeds were deprived of their germinating power 

 by this treatment. Detmer has made similar observations 

 with the same results. 



A remarkable illustration of the extent to which dry seeds can with- 

 stand the injurious influence of extreme cold is afforded by C. de 

 Candolle's observations. He exposed seeds of a number of species of 

 plants for about two hours to a temperature of 80 C., obtained by the 

 evaporation of liquid sulphur dioxide and nitrous oxide, and he found 

 that none of them lost their power of germinating. 



With regard to other plants, Cagniard de la Tour ascertained that dry 

 Yeast may be exposed to the temperature of solid carbon dioxide ( 60 C.) 

 without being killed, whereas, in the moist state, a temperature below 

 50 C. proves fatal to it : Cohn found that Bacteria were not killed by 

 exposure for five hours to a temperature of -ioC. which sank, some- 

 times, as low as -i8C. Probably the Schizomycetes and Saccharo- 

 mycetes cannot be killed by cold, for Schumacher has found that they 

 survive exposure to a temperature of - ii37C. 



