110 M. Dutrochet on the Tempemtitre of Vegetables. 



mentioned above, and whose results were contradictoi'y ; they 

 proved to me, that there was a source of error in the employ- 

 ment of the mode of experimenting pointed out to me by M. 

 Becquerel ; a mode of experimenting, whose principle never- 

 theless was good, but which required an addition. The ob- 

 ject was to put an end to the evaporation which was an in- 

 cessant cause, variable and unequal, of cooling for the two 

 branches ; and I obtained it by placing these tAvo branches, 

 the one dead and the other living, and both green, in a large 

 matrass, closed by a cork, at the bottom of which there was a 

 little Avater intended to saturate by [its evaporation the air 

 contained in it, and to support the life of the plant plunged 

 into this liquid at its lower extremity. The evaporation of 

 the fluids contained in the two branches being thus suspend- 

 ed, and consequently this cause of cooling no longer existing, 

 the heat proper to the living branch exhibited itself ; and it 

 must not be supposed that it is the unequal evaporation of the 

 living branch which, continuing to take place in the close ves- 

 sel, was the cause of the greater degree of heat manifested by 

 this last, for its higher temperature exhibited itself in the 

 same way when the dead branch, full of its organic fluids, 

 Avas replaced by a dried branch. HoAvever, I could not with 

 confidence have made use of dried branches in my experi- 

 ments, because these branches, in the cells and ves.sels of 

 Avhich the air had replaced the organic liquids, ought on that 

 account to be less easily permeable to heat than the living 

 branches full of fluid, so that they Avere not suited to acquire 

 at the same time the variations of the surrounding heat. I 

 could not thus hope from their employment results so exact as 

 those which might be afforded me by using green branches 

 depriA^ed of life. 



It will thus be perceived Avhat I OAve to the adAdce of M. 

 Becquerel, and I am glad to acknowledge my obligation ; but 

 he will, I hope, agree Avith me that the process of experi- 

 menting, such as he recommended to me, and such as he em- 

 ployed himself, carried along Avith it causes of error. I am 

 not afraid therefore to affirm, that it is by the effect of these 

 causes of error that he has found in a living branch of a tree 

 a temperature higher by some degrees than that presented at 

 the same time by a dead branch. The heat of branches is 



