M. Dutrochet on the Temperature of Vegetables. 105 



maximum. Now, as it is then that vegetables produce the 

 gi'eatest quantity of oxygen "which is introduced into their 

 pneumatic and respiratory organs, it follows that their produc- 

 tion of heat is in proportion with their respiration, in a similar 

 manner as with animals Finally, the heat which vegetables 

 manifest Avhen surrounded with an atmosphere satm-ated with 

 water, is only a part of the total heat Avhich they produce, 

 since another portion is necessarily absorbed by the produc- 

 tion of oxygen under the influence of the light. All my ex- 

 periments were made in diffuse light. 



A'dcUtional Note on the Temperature of Plants. By 

 M. Dutrochet.* 



The delay of a year in publishing these observations, was 

 caused by the fear of having been led into error by an instru- 

 ment which is the soui'ce of many deceptions, against which 

 it was necessai'y carefully to guard. The thermo-electric 

 apparatus I employed last year, gave 6° of deviation of the 

 magnetized needle, for one centesimal thermometric degree of 

 difference of temperature between the two cemented points ; 

 this year, furnished Avith an excellent galvanometer of Gour- 

 jon, I obtain 16" of deviation of the magnetized needle, for 

 one centesimal degree. Provided with so sensible a thermo- 

 electric apparatus, I have repeated, Avith less chances of error, 

 and with much more precision, my observations of last year, 

 and have fully verified theu* accuracy. The apparatus I used, 

 and a figure of which I have given, is only proper for cut 

 plants, whose life is maintained by the cut end being im- 

 mersed into water. This year I employed a more perfect 

 apparatus, with which I can subject to observation not only 

 cut i»lants, but also plants still grooving in the ground. I will 

 give, in the memoir I am about to publish, a description of 

 this new apparatus, constructed on the same principles as the 

 former, but in which the glass vessel employed formerly has 

 been replaced bj^ a high cylindrical bell-glass. My needles 

 are difi^erently constructed from those I used last year. They 

 are made of very fine copper and iron wires, bent back on 

 themselves, at a very acute -angle, where they are soldered 



* Communicated to the French Academy of Sciences, in June 183(l. 



