THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



JULY 1842. 



I. On the Influence of the Dew-point on Vegetables, considered 



especially with reference to their Temperature. By D. P. 



Gardner, M.D., Professor of the Physical Sciences, fyc. in 



Hampden Sidney College, tyc, Corresponding Member of the 



New York Lyceum qf Natural History*. 

 HPHE object of this paper is to establish the mutual relation 

 existing between the temperature of plants f, their eva- 

 poration, and the amount of vapour existing in the atmosphere. 

 The subject will be examined under four heads, which have 

 been suggested by the results of the experiments instituted, 

 and are therefore gradual developments of the proofs by which 

 the connexion between the dew-point and temperature of 

 plants is sought to be established. 



1st. Certain vegetables are without any specific heat. 



2ndly. The variations plus or minus the atmospheric tem- 

 perature observable in plants are owing chiefly to the state of 

 the dew-point, its elevation causing an increase of heat by 

 checking evaporation, and its depression by favouring evapo- 

 ration producing coldness ; in other words, the rate of evapo- 

 ration, and its effect in producing a decrease of temperature in 

 plants, is directly as the greatness of the drying power, and 

 inversely as its diminution. 



3rdly. The sensible heat of plants is directly as the atmo- 

 spheric temperature, and the chemical action going on in their 

 cells ; and inversely as the evaporation, radiation and conduc- 



* Read before the Linnsean Society, November 16th, 1841, and now com- 

 municated at the request of the Author, by J. J. Bennett, Esq., Sec. L.S. 



t On the subject of the heat of plants, see Meyen's Report for 1839, in 

 the Annals and Magazine of Natural History, vol. viii. p. 27 ; also the 

 original paper by Vrolyk and De Vriese, in the same work, vol. vii. p. 161 

 — Edit. 



Phil, Mag, S. 3. Vol. 21. No. 135. July 1842. B 



