30 Meyen's Report for 1839 on Physiological Botany. 



years ago. The observations were made in company with M. 

 Mirbel in the botanical garden on the twigs of an Acacia : ob- 

 servations on dead and living boughs gave directly the most 

 striking differences of temperature. In the following year 

 M. Dutrochet wished to institute similar experiments, and 

 made use of the advice and experience of M. Becquerel*. In 

 the sitting of the Academy of 1st of July, M. Dutrochet re- 

 plied to the statements of M. Becquerel, and endeavoured to 

 show that his observations by no means proved with certainty 

 the existence of a peculiar heat in plants. 



MM. Bergsma and van Beckf 5 in consequence of Dutro- 

 chet' s researches, have sent a letter to the Academy at Paris, 

 in which they describe their new experiments on the heat of 

 vegetables, by which it is clearly proved that the transpira- 

 tion is the cause of the difficulty in measuring the peculiar 

 temperature. They chose (in January 1839) a hyacinth 

 growing in a glass for their experiments. The glass was put 

 into another vessel containing water of a higher temperature, 

 in order in this manner to increase the activity of the roots. 



The needles of the thermo-electrical apparatus were then 

 inserted into the external parts of the flower-stalk, and in- 

 stead of an increase of temperature, they observed a fall ; the 

 apparatus exhibited, viz. 17*5° C, while that of the water was 

 28*5°. The experiment was repeated several times with like 

 success, as also with the pedunculus of Entelea arborescens, 

 R. Br. This phenomenon is explained by the powerful eva- 

 poration which is caused by the increased activity promoted 

 by the warm water. When the needles were inserted into the 

 middle of the flower-stalk of the hyacinth, the temperature of 

 the interior was found to be 1° higher than that of the sur- 

 rounding air. 



All the above treatises of Dutrochet, Becquerel, Bergsma, 

 and van Beck, are to be found in the August number of the 

 e Annales des Sciences Naturelles/ 



On the 21st of November M. Dutrochet J communicated 

 to the Academy some new observations which he had made 

 during the previous summer on the heat of vegetables ; he 

 states generally that plants possess a peculiar heat, which is 

 principally located in the green parts. This heat exhibits a 

 daily periodicity; it reaches its maximum towards midday, and 

 its minimum during the night. M. Dutrochet communicated 

 his special experiments on different plants, from which the 

 daily variations of temperature may be recognised, e. g. in 



* Comptes Rendus de 1 Juillet, p. 4 7. t Ibid., 2 Septembre, p. 328. 

 J Ibid., 18 Nov., p. 613. 



