8o THE LIFE OF THE PLANT 



found germinating ; their tiny rootlets were piercing 

 through the ice. This strange, unexpected but quite 

 authentic experiment, as well as similar facts concerning 

 the blossoming of some alpine plants, which flower even 

 in the snow, are probably to be explained by the fact 

 that heat is generated by the respiration of plants and 

 is capable of melting ice in the immediate neighbourhood 

 of the plants in question. Life was formerly considered 

 impossible at 32° F., among other reasons, because 

 water should freeze at that temperature ; but this is a 

 mistake, for it is known that water may not freeze even 

 at a temperature below 32° ; for instance, it does not 

 freeze even at 10° F. in very narrow capillary tubes. 



We see, then, that germination (and, generally 

 speaking, this is true of all vital processes) can take 

 place only within the narrow range of temperature 

 between the limits 32° and 104° F. These limits do not, 

 however, apply to resting seeds. Owing to their dryness 

 they are able to bear without injury much greater 

 extremes of temperature. When thoroughly dried 

 seeds can be exposed on the one hand to such high 

 temperatures as 25o°-320° F., and on the other hand to 

 very low temperatures, obtained by means of liquid 

 air, without losing their capacity for germination. 

 A resting seed is thus distinguished by possessing to a 

 remarkable degree the power of enduring great extremes 

 of temperature, and this endurance constitutes one of its 

 important attributes. 



Such is the significance of heat, the third factor by 

 which germination is conditioned. We must not, 

 however, suppose that the accelerating effect of heat, 

 the repressing influence of cold, and the fact of limits of 

 temperature, constitute a peculiarity of living organisms 

 as such. On the contrary, we know that the majority 

 of the chemical and physical processes at work in it 

 depend on the temperature. With an increase of 

 temperature, diffusion and the conduction of liquids are 



