CHAP. VIII. SEED. 301 



than any other at the first dawn of its hfe. If, says De 

 Candolle, the temperature is too high, germination proceeds 

 too rapidly, and the result is weak and languishing plants, 

 in which we cannot avoid recognising beings too much excited 

 and badly nourished. If the temperature is too low, the ex- 

 citement is not sufficient, and it often happens that the seed 

 cannot resist the decay induced by the water it has absorbed 

 but not assimilated. It is between these limits that a suitable 

 temperature for every species is to be sought. 



Edwards and Colin have instituted some experiments to 

 determine what temperature seeds can bear. They found that 

 Wheat, Barley, and Rye could germinate at 7° Cent. 

 44''6 Fahr.) ; and that grain of the same description did not 

 apparently suffer by being exposed for a quarter of an hour 

 to a temperature equal to freezing mercury : such grains were 

 afterwards placed in a proper situation, and germination took 

 place as usual. Considering that the particles of foecula of 

 which seeds consist are not liable to bursting below a tem- 

 pei'ature of 75° Cent. (167° Fahr.), these observers were led 

 to ascertain how near an approach to this extreme tempera- 

 ture might be made without destroying vegetable life. Seeds of 

 various cereal and leguminous plants were placed for a quarter of 

 an hour in water of this temperature, and they were all killed ; 

 five minutes were afterwards ascertained to suffice for the de- 

 struction of three in five. Less elevated temperatures were next 

 experimented on : Wheat, Barley, Kidney Beans, and Flax 

 were killed in 27^ minutes by water at 62° Cent. (143°6 Fahr.) 

 a few grains of Rye and some Beans required a longer expo- 

 sure to be destroyed. When the temperature was lowered to 

 52° Cent. (125°6 Fahr.) most of the seeds in experiment re- 

 tained their vitality; but even this was fatal to Barley, 

 Kidney Beans, and Flax. 



Fluid water has conducting powers very different from those 

 of vapour or of dry air ; it was thereupon important to deter- 

 mine Avhether the temperature that seeds can bear is regulated 

 by the nature of the medium in which they are exposed to it. 

 In vapour 75° Cent. (167° Fahr.) were sufficient to destroy 

 such seeds as were exposed, but at 62° Cent. (143°6 Fahr.) 

 they retained their vitality after having been under experiment 



