LEAVES ON THE ATMOSPHERE. 213 



ance of the animal and vegetable kingdoms 

 on each other, which had never been sus- 

 pected before his time. Comparative expe- 

 riments upon the lower tribes of these king- 

 doms have not yet been made, but they 

 would probably afford us a new test for di- 

 stinguishing them. The air so copiously pu- 

 rified by a Conferva, one of the most inferior 

 in the scale of plants, may be very extensively 

 useful to the innumerable tribes of animated 

 beings which inhabit the same waters. The 

 abundant air-bubbles which have long ago 

 given even a botanical name to one supposed 

 species, Conferva bullosa, are probably a 

 source of life and health to whole nations of 

 aquatic insects, worms and polypes, whenever 

 the sun shines. 



In the dark, plants give out carbon and 

 absorb oxygen : but the proportion of the 

 latter is small, compared to what they exhale 

 by day, as must likewise be the proportion 

 of carbon given out; else the quantity of 

 the latter added to their substance would be 

 but trifling, especially in those climates 

 where the proportion of day to night is nearly 

 equal, and which, notwithstanding, we know 



