210 KECENT RESEARCHES ON THE RESPIRATION OF PLANTS. 



The buds, selected from amongst the finest and cut witli a small 

 disc of the branches bearing them, were made up into a little 

 bundle in such a way that the small discs formed a support 

 which could be plunged into water and yet leave the buds un- 

 wetted. A cup of water with the buds thus arranged within it 

 was placed under a graduated bell-glass, the inside of wliich liad 

 been previously covered with a concentrated solution of hydrate 

 of potash in order that the carbonic acid might be fixed at the 

 moment of its escape ; the bell-glass and the cup within it were 

 then put in a dish of water placed near the window of a room 

 the temperature of which was kept at 15° or 16° C during 

 the twenty-four hours for which the experiment lasted. The 

 buds did not suflfer the least under these circumstances, and 

 whilst under the glass their little scales expanded, and the size 

 of the small leaves lying immediately below the scales of the 

 strongest buds, as those of the Mihes, Tilia, Staphylea, &c., was 

 doubled. 



The diminution of the volume of air was noted separately, day 

 and night ; the temperature being the same, this diminution very 

 nearly expressed the volume of carbonic acid given out ; for it 

 had been previously ascertained that the air was condensed by 

 the buds only to a very insignificant extent. 



The experiment over, the buds were separated from the small 

 discs which supported them, weighed when quite fresh, then 

 dried for twelve hours at a temperature of 110° C, and weighed 

 dry. 



The annexed table (p. 211) shows that in equal times and tem- 

 peratures buds consume on an average twice as much carbon as 

 fully developed leaves. This accounts for the fact, that in the 

 buds and their vicinity M. Dutrochet was enabled to determine 

 in a most marked manner the temperature peculiar to plants, and 

 to generalize the discovery of their paroxysm made by M. Ad. 

 Brongniart. 



If the numbers in the three last columns be compared, it will 

 be seen that as a general rule, and under the conditions men- 

 tioned, the buds exhale about eight times their volume of car- 

 bonic acid in the twenty-four hours ; that dried at a temperature 

 of 110° C. they lose on an average five-fourths of their weight, 

 a loss which represents their water of composition and of vege- 

 tation, and that then the carbonic acid exhaled is to the volume 

 of their solid parts as 40 to 1, if we admit, as we may witli con- 

 siderable accuracy, that in this state their density is the same as 

 that of water. 



Theodore de Saussure was satisfied with establishing the re- 

 lation in volume which the carbonic acid expired by leaves bore 

 to their weight wlieii fresh. In our opinion no exact results 



