16 CORRELATION OF VITAL 



the air by their leaves, or obtaining it through their rootlets. In 

 the latter case they may obtain it from rains which have fallen 

 to the earth impregnated with the carbonic acid of the atmosphere, 

 or else they procure it from that which is liberated by the gradual 

 decomposition of organic particles in the soil. But that the air 

 is the great storehouse whence, either mediately or immediately, 

 plants procure their carbon, is rendered more and more obvious to 

 us by the consideration of such facts as those to which Schleiden 

 refers in his " Biography of a Plant " when he says : — " From 

 forests maintained in good condition we annually obtain about 

 4,000 lbs. of dry wood per acre, which contains about 1,000 lbs. 

 of carbon. But we do not manure the soil of the forests, and its 

 supply of humus, far from being exhausted, increases considerably 

 from year to year, owing to the breakage by wind and the fall 

 of the leaf. The haymaker of Switzerland and the Tyrol mows 

 his definite amount of grass every year on the Alps, inaccessible 

 to cattle, and gives not back the smallest quantity of organic 

 substance to the soil. Whence comes this hay if not from the 

 atmosphere ? The plant requires carbon and nitrogen, and in the 

 woods and on the wild Alps there is no possibility of its acquiring 

 these matters save from the ammonia and carbonic acid of the 

 atmosphere." 



As Dumas says : — " It is in plants, consequently, that the true 

 laboratory of organic nature resides ; carbon, hydrogen, am- 

 monium, and water are the elements they work upon ; and 

 woody fibre, starch, gums, and sugars, on the one hand, fibrine, 

 albumen, caseum, and gluten, on the other, are the products that 

 present themselves as fundamental in either organic kingdom of 

 nature — products, however, which are formed in plants, and in 

 plants only, and merely transferred by digestion to the bodies of 

 animals." 



Such, then, is the mighty round of things, such are the inter- 

 changes ever taking place on the surface of our globe. The 

 inorganic is continually being fashioned into the organic, and 

 this after passing through successive changes, and after having 

 displayed the manifestations of Life, is ever passing again into the 

 inorganic, ever again giving up its fashioning forces. " The crude 

 and formless mass of the air gradually organised in vegetables, 

 passes without change into animals, and becomes the instrument 

 of sensation and thought ; then vanquished by this effort, and, as 

 it were, broken, it returns as crude matter to the source whence 



