262 HEAT OF GEKMINATION. [BOOK 11. 



by the authors now quoted, to be a fact of the first importance. 

 (Comptes renduSj vii. 922.) 



It also appears that the carbon of seeds is lost, not only by 

 the formation of carbonic acid, but by the production of 

 acetic acid, during germination, a phenomenon which Messrs. 

 Becquerel and Boussingault consider constant. (Comptes 

 renduSj vi. 109.) 



In the opinion of some persons, oxygen also acts as a 

 stimulant of the vital actions of the embryo. Humboldt 

 remarked that seeds plunged in chlorine, and taken out 

 before the radicle appears externally, germinate more rapidly 

 than ordinary ; Cress, for instance, may thus be made to 

 germinate in six hours instead of twenty-four or thirty. He 

 even succeeded, by this process, in bringing about germination 

 in old seeds which appeared destitute of the power. These 

 experiments have not, however, succeeded in all hands : in 

 many cases it is possible that the success that is said to have 

 attended them has been imaginary j and, as the theory upon 

 which the action of chlorine was explained is now abandoned, 

 one cannot avoid entertaining doubts as to the accuracy of 

 the alleged fact. 



It is heat in which the stimulus necessary to call the 

 vitality of seeds into action seems really to reside. No seed 

 can germinate at a temperature so low as that of freezing ; 

 and each seems to have some one temperature more proper 

 for it than any other, at the first dawn of its life. If, says 

 De Candolle, the temperature is too high, germination pro- 

 ceeds 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 excitement 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 centig. 

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



