38 I>K. SCHLEIDEN'S THEOKY OF AGEICULTUKE. 



If we reflect again on the constant outgoing from an estate 

 in various forms, and the extremely small quantity of matter 

 \vhich conies in to replace the expenditure, it is easy to see that 

 all virtue would be extracted in a very short time from the land 

 if plants depended, even in a small degree, only on the organic 

 substances ; whereas under good cultivation the ground is con- 

 stantly improved in quality. Indeed, from the observations of 

 the best authorities, it appears that the ground produces three 

 times as much organic matter as it receives. But more than 

 this, the greater part of the organic substance of manure cannot 

 enter into the produce. The land is manured not for the year 

 only, but for a series of years. By far the greater portion passes 

 off by a silent process of decomposition, especially when the 

 land is stirred, into the surrounding atmosphere. Not a tenth 

 part of the organic substance of plants can possibly be supplied 

 by the decay. There is, however, no ground to suppose that 

 this tenth part arises from a different quarter from the remain- 

 ing nine in cultivated plants, and the whole ten in a state of 

 nature. 



When it was stated above that plants of husbandry are dis- 

 tinguished by an alteration in the chemical process, this did not 

 necessarily imply a change in quality. Wild plants form from 

 water, carbonic acid, and ammonia, albumen, gluten, sugar, 

 starch, oil, &c. The same substances are formed in cultivated 

 plants ; they do not form peculiar secretions, but merely store 

 up some particular substance in excess. 



Nor shall we find the matter weakened if the elements con- 

 cerned in nutrition be severally examined. Oxygen and hydrogen 

 need not be here considered, as they are amply supplied by 

 water. Attention, therefore, may be confined to carbonic acid, 

 nitrogen, sulphur, phosphorus, and the inorganic ashes. 



1. Carbon is doubtless the most important constituent; it 

 forms half the substance of the dry plant, and eight times as 

 much as the nitrogen ; the whole question therefore turns on 

 the absorption of carbon. As in general the organic matter of 

 the earth cannot supply the exigencies of the whole plant, so 

 neither can it satisfy its demand of carbon. 



Sugar plantations receive no manure in general, or at least 

 merely the ashes of the spent canes. An acre produces 7500 lbs. 

 of cane, the expressed juice of which contains at least 700 lbs., 

 and the fragments of cane 500 lbs. of carbon. There is there- 

 fore an expenditure of 1200 lbs. of carbon per acre without any 

 compensation. 



The Oil palms grow in sand destitute of humus. Thirty- 

 three million poimds of carbon are produced annually on ground 

 free from organic matter in this way alone. 



