42 now .Rops PKKD. 



tions of carbonic acid mixed with atmospheric air on the 

 development of ^ egetation. lie found that young peas (4 

 inches high) when exposed to direct sunlight, endured for 

 some days an atmosphere consisting to one-half of carbonic 

 acid. When the proportion of tliis gas was increased to 

 two-thirds or more, they speedily Avithered. In air con- 

 taining one-twelfth of carbonic acid the peas flourished 

 much better than in ordinary atmospheric air. The aver- 

 age increase of each of the plants exposed to the latter 

 for five or six hours daily during ten days was eight 

 grains ; while in the former it amounted in the same time to 

 eleven gi-aiiis. In the shade, however, Saussure found that 

 increase of the proportion of carbonic acid to one-twelfth 

 was detrimental to the plants. Their growth under these 

 circumstances was but three-fifths of that experienced by 

 similar plants exposed to the same light for tlie same time, 

 but in common air. He also proved that foliage cannot long 

 exist in the total absence of carbonic acid, w'hen exposed 

 to direct sunlight. This result was obtained by enclosing 

 young plants whose roots were immersed in water, or the 

 branches of trees stationed in the soil, in a vessel which 

 contained moistened quicklime. This substance rapidly 

 absorbs and fixes carbonic acid, forming carbonate of lime. 

 Thus situated, the leaves began in a few days to turn yel- 

 low, and in two to three weeks they dropped ofi". 



In darkness the presence of lime not only did not de- 

 stroy the plants, but they prospered the better for its 

 presence, i. e., for the absence or constant removal of car- 

 bonic acid. 



Boussingault has lately shown that pure carbonic acid 

 is decomposed by leaves exposed to sunlight with extreme 

 slowness, or not at all. It must be mixed with some other 

 gas, and when diluted with either oxygen, nitrogen, or hy- 

 drogen, or even when rarefied by the air-pum]) to a certain 

 extent, the absorption and decomposition proceed as usual. 



Conclusioilt — It thus is proved list, that vegetatioa 



PHOPERTY OF 



1' 1. u rni t Pnr \ \vxtktN!\ 



