i«fh ^7; . M- Van Beck on Temperature of Plan(f.. . . , 3^ 

 bell-glass which cut off all communication between the air of 

 the apartment and that of the plant, the heat of the latter al- 

 ways rose suddenly some tenths of a degree. This pheno- 

 menon, however, lasted only a few minutes ; the magnetic 

 needle soon retrograded, passing zero of the scale, and shew- 

 ing by its opposite and permanent deviation, that the living 

 plant had a much lower temperature than the dead leaf, as is 

 always the case in the atmosphere. 



Is this phenomenon to be ascribed to the instantaneous ac- 

 cess of the free air to the plant, which, by stimulating its vi- 

 tal functions, which were depressed by its having been kept 

 in a less pure air, augments at the same time its proper heat, 

 before the counteracting and frig orific influence of re-established 

 evaporation has had time to make itself felt ? 



This I cannot venture to decide ; but I hope that other phi- 

 losophers and naturalists will engage in these researches, 

 which, if I am not deceived, may yet throw light on many an 

 interesting question in vegetable physiology.* 



* Note occasioned by the Obsertations of M. Van Beck, oti the proper Tempera- 

 ture of Plants. By M. Dutrochet. 



I ought to return my thanks to M. Van Beck, for the eagerness he has 

 shewn in repeating my experiments on the internal heat of vegetables. 

 His verification of the existence of this heat, and its diurnal period, hence- 

 forth places these facts in the number of those definitively established in 

 science, which in general admits only of such as have been seen by more 

 than one observer. 



IVL Van Beclc diflers from me in regard to one matter of very little im- 

 portance. I have stated that when making a comparative trial in the open 

 air of a living vegetable, and another of a similar kind in a dead state, that 

 the latter always ai^peared colder than the former ; M. Van Beck always 

 obtained an opposite result. This difference in the result of our observa- 

 tions is perhaps owing to a diftbrence in the mode of prepai-ing the experi- 

 ment. M. Van Beck, like myself, plunged tlio pai-t of the vegetable he 

 wished to kill into very warm water ; perhaps he then left it to cool in the 

 open air, and thus lose by evaporation a part of the water which moistened 

 its surface. In my case, in was cooled by immersion in cold water, and in 

 this condition, completely saturated, it was subjected to experiment It 

 may rcidily be conceived, that there must have been more evaporation in it 

 than in the less huujid living vegetable, and that, consequently, it must 

 VOt. XXVIII. NO. LVI. — Al'UlL 1840. Z 



