136 THE BEGINNINGS OF LIFE. 



their carbon, is rendered more and more obvious to us 

 by the consideration of such facts as those to which 

 Schleiden refers when he says 1 : c From forests main- 

 tained in good condition we annually obtain about 

 4000 Ibs. of dry wood per acre, which contains about 

 1000 Ibs. 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, inacces- 

 sible 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. 3 



How important such facts as these are in throwing 

 light upon the past history of our globe, when we 

 attempt to study it with the aid of those relics, 

 preserved as fossil plants and animals, and dis- 

 tributed through the various successive strata of its 

 crust, the palaeontologists are best entitled to inform 

 us. M. Ad. Brongniart, one of the most able and 

 eloquent of these, even so long ago as the year 1838 

 announced, before the Academy of Sciences, the fol- 



1 ' Biography of a Plant.' 



