174 CHEMICAL ACTIO >r 01" 



botanical name to one supposed species, Conferva bulh- 

 sa, are probably a source of life and health to whole na- 

 tions of aquatic insects, worms and polypes, whenever 

 the sun shines. 



In the dark, plants give out carbon and absorl) oxy- 

 gen : but the proportion of the latter is small, compared 

 to what they exhale by day, as must likewise be the pro- 

 portion of carbon given out ; else the quantity of tlie lat- 

 ter added to their substance would be but trifling, es- 

 pecially in those climates where the proportion of day to 

 night is nearly equal, and which, notwithstanding, we 

 know to be excessively luxuriant in vegetation. Plants 

 also give out azotic gas : but M. de Saussure is of 

 ©pinion that this proceeds from their internal substance ; 

 and it appears by his experiments to be father a sign of 

 disease or approaching decay, than a regular chemical 

 production of their constitution when in health ; for 

 Sennebier found the quantity of oxygen emitted was in 

 proportion to the thickness of the leaf, or quantity of 

 parenchyma. Yet the parenchyma must be in its orig- 

 inal organized state, for when bruised its functions are 

 destroyed. 



Possibly such an alternation in the functions of vege- 

 tables between day and night may afford a necessary 

 repose to their vital principle, whose share in them we 

 know to be of primary importance. Whatever may 

 happen to plants in the dark, there can be no doubt of 

 their principal business in the oeconomy of nature being 

 what we have described. The most luminous and com- 

 pendious view of the whole subject is given by Dr. 

 Thomson of Edinburgh in the fourth vol. of his Chetn- 



