ORIGINAL COMMUNICATIONS 



XIX. — Recent Researches on the Respiration of Plants. By 

 M. Garreau, M.D.* 



In the course of my first experiments upon the absorption by 

 and exhalation from those surfaces of plants which are exposed 

 to air, I had often noticed that the leaves and green parts of 

 plants, when acted upon by the direct rays of the sun, gave out 

 very sensible quantities of carbonic acid. 



This fact, so apparently opposed to the ordinary notions re- 

 specting the functions of leaves, struck me very forcibly, espe- 

 cially as it is also precisely under the direct influence of the 

 sun that the leaves and young shoots of plants reduce the carbonic 

 acid in the atmosphere with the greatest rapidity and retain the 

 carbon. 



Some more recent experiments made in the latter part of 

 1850 {Annalesdes Sciences Naturelles, 1851) not only confirmed 

 my former observations, but showed that expiration of the acid gas 

 takes place equally in the shade if the temperature is sufficiently 

 high to cause the vital juices of the plants to move. These ex- 

 periments being made towards the end of the summer, did not 

 enable me to ascertain whetlier the phenomena which I have men- 

 tioned were affected by the age of the plants or the seasons, and 

 for the purpose of acquiring further information upon this sub- 

 ject the experiments about to be described were made. 



1. The Action of Buds on Atmospheric Air. 



Buds, like young plants, represent individuals at a time when 

 tlie living substances containing proteine are, comparatively 

 speaking, much greater than at any other time of their existence, 

 and it became interesting to ascertain whether the activity of 

 their respiration bore any ratio to the quantity of their animal 

 matter. 



In order that the results might be as exact as possible and 

 easily compared with eacli other, the degree of the develope- 

 ment of the buds, and their weight both when fresh and dried, 

 were noticed with the greatest care, as was also the quantity of 

 air in which they respired, wdiich was always kept as nearly as 

 possible at the same temperature during all the experiments. 



* Annales des Sciences Naturelles, xvi. 271. 

 VOL. VII. Q 



