INFLUENCE OF THE ATMOSPHERE. 77 



tain it with great force, (probably because they emit little or 

 no carbonic acid). The various species of these plants, ac- 

 cording to the experiments of Saussure, absorb during the 

 summer months, jfrom 1 to 1.7 of their bulk of oxygen ; hence, 

 such plants will flourish on high mountains, where the air is 

 rarified, and on arid sands. 



The leaves of evergreen trees are next in order, as they ab- 

 sorb more oxygen than the fleshy-leaved plants, and much 

 less than those trees which lose their leaves during the win- 

 ter. The quantity in this class, varies during the months of 

 May and June from 1.5 to four times their volume, and dur- 

 ing the month of September from 0.86 to 3 times their 

 volume.* 



Of the herbaceous plants^ those which grow on marsh- 

 es and bogs, absorb but little oxygen gas. This may be 

 due to the fact, that they are surrounded by an atmosphere 

 of vapor, or of carbonic acid, which does not render the in- 

 troduction of oxygen necessary. The quantity in such plants 

 under similar circumstances varies from 0.7 to 2.3 times 

 the volume of the leaves, while the leaves of herbaceous 

 plants not aquatic, absorb from 0.66 to 5 times their vol- 

 ume. 



The leaves of those trees which are nailed during the win- 

 ter, as the oak, maple, and most fruit trees, absorb the larg- 

 est quantity of oxygen, and contain the most carbon. This 

 seems to depend upon the nature of the substances formed in 

 the leaf; thus the tasteless leaves of the Agave Americana ab- 

 sorb only 0.3 of their volume in the dark during twenty-four 

 hours; those of the oak containing tannic acid, fourteen 

 times as much ; and the balmy leaves of the poplus alba twen- 

 ty-one times that quantity. The large quantity of oxygen, 

 absorbed by these plants, may, also, be partly due to the fact, 

 that they not only supply nourishment for the purposes of veg- 



Thompson's Chemistry, Organic bodies, p. 999. 



7 



