M. Dutrochet on the Temperature of Vegetables. Ill 



iiever so mucli elevated, foi', at its maximumj it only reaches 

 one-third of a degree, according to my observations. Besides, 

 I must here add, that numerous experiments have proved to 

 me, that it is only the branches in a soft or herbaceous state 

 which have heat proper to themselves. I have never found 

 the slightest trace of proper heat in the ligneous tissue of 

 trees ; and my thermo-electric apparatus indicates, without dif- 

 ficulty, the existence of ^^ of a centesimal degree of heat, cor- 

 responding to ^ of a degree of deviation of the magnetic needle 

 of the multiplicator. I have observed the proper heat of 

 young branches of many trees or shrubs such as the Aylan- 

 thus gland tdosa, Desf. and the common elder (Sambucits ni- 

 gra), branches having a sufficient size, in their herbaceous 

 portion, to be submitted to this kind of experimenting. This 

 herbaceous part, that is to say the upper merithalles, alone ex- 

 hibited a proper heat ; I found no trace of it in the lower me- 

 rithalles, whether the soldered point was placed in the pith or 

 in the ligneous tissue. Of course, I found no proper Iieat in 

 the ligneous tissue of the older branches. 



To conclude, I do not hesitate to affirm, that the heat per- 

 ceived in the branch of a tree by Messrs Becquerel and 

 Mirbel was not the proper and vital heat of that branch: 

 whence it follows that no one before me has demonstrated or 

 even ascertained the existence of this vital heat in the branches 

 of plants, for I regard as null the researches which have been 

 made on this subject by placing thermometers in holes formed 

 in the trunks of trees.* 



~ On the IStli November 1839, M. Dutrocliet read a notice containing an 

 account of new researches whicli he lias made with the thermo-electric ap- 

 paratus, on the vital licut of plants. They confirm the observations com- 

 municated in the preceding paper. Thus, it would appeiir certain, that all 

 plants have a pro^jer and vital heat ; that this heat exists especially in the 

 green pai'ts ; and lastly, that it undergoes a quotidian paroxysm, which 

 reaches its maximum during the day, and its minimum during tlio night. 

 The following are the most striking facts contained in the new communica- 

 tion : The Euphorhia lothyrh is the plant, a stalk of which has afforded tlie 

 greatest degree of vital heat. The hour of the quotidian maxinmm is always 

 about the same for each plant. This hour varies from 10 o'clock in the 

 morning till 3 o'clock in the afternoon, in diflforcnt plants. No proper 

 heat has been detected in ligneous tissue, even in that of recent formation. 

 Complete darkness does not prevent the reproduction of the diurnal pa- 

 roxysm of the proper heat of the stalks of plants, and that during some 

 days; but it goes on gi-adually dimiuishhig it's iutcusity, till the complete 

 extinction of thiy vital hcut. 



