THE VEGETABLE KINGDOM. 415 



ment, approaching more that exhibited by fiwh, which have 

 a special respiratory apparatus, the branchicie, so disposed 

 as to take up imperceptible portions of air contained in 

 the Avater in large enough quantity to suffice for their re- 

 spiration. An analogous disposition is seen in certain 

 plants of the family of the naiads, Naiadese,^ which live in 

 our pools and ditches. Their leaves are unprovided with 

 epidermis, and represent a kind of branchise, constructed 

 to act upon the airy particles contained in the medium in 

 which they live. Of this class are the potamogetons 

 or pond-weeds, which, in respect to their respiration, con- 

 sidered in an isolated point of view, are in reality fish-plants. 



The respiration of animals is injurious to the composi- 

 tion of the atmospheric air; they vitiate it incessantly, 

 either by absorbing the vital principle oxygen, or hj dif- 

 fusing in it a deadly poison — carbonic acid. 



It has been calculated that the human species alone con- 

 sumes annually 100,000 millions of cubic metres (or yards) 

 of oxygen, and that animals cjuadruple this amount. 



On the other hand, every man exhales daily 250 

 grammes (8 oz. 1 dwt. 1 gr. troy) of carbonic acid gas, 

 which gives about 75 grammes (2 oz. 4 dwt. 6 22 gr. troy) 

 of combustible carbon. Hence, without reckoning the 

 amount produced by animals, the quantity of carbon 

 poured into the atmosphere by the population of France 

 alone has been computed at 2,500,000 tons French 

 (2,454,546 tons avoirdupois). 



This alarming alteration in our atmosphere is enough 

 to startle one; it seems as if it must bring on an entire 

 destruction of animal life. But by the side of the disturb- 

 ing element Providence has placed the means of repara- 

 tion; the mantle of verdure on the globe remedies all the 



' Also called Fluviales, a small natural order of endogena.- Tr. 



&3 



