120 



ROYAL HORTICULTURAL SOCIETY. 



If, then, "water does not act by means of its chemical constituents 

 as nutritive matter for plants, it can serve only as the means of 

 conveying those nutritive substances which are dissolved in the 

 water. "We have spoken of the humous extract dissolved in the 

 water as the peculiar nutritive substance of plants, and especially 

 the different, in fact, nitrogenous humates which are found in it, 

 and which, according to the experiments contained in the treatise 

 on the discovery of the true nutriment of plants, are the only 

 source of the oxygen which is exhaled under the influence of 

 light. The ground is therefore the only magazine of nutriment 

 for plants, the water the bearer of the nutritive matter dissolved 

 out of the ground. All necessary ingredients for the organic 

 formation of the tissues of plants must be contained in the 

 humous matters, to which the mineral salts are only added as 

 stimulants and promoters of assimilation. Carbon, hydrogen, 

 nitrogen, and oxygen, and even sulphur and phosphorus are con- 

 tained in humus as matters of nutriment ; plants need no nutri- 

 tive matter from the air ; they can imbibe only water from it in 

 order to maintain their full flow of life (Entd. der wahren Pflan- 

 zennahrung, pp. 140-141). 



Liebig contends that humus cannot be the nutritive matter, 

 inasmuch as he considers it impossible that the necessary quantity 

 of humic acid or humate of lime could be dissolved in the water. 

 An acre of land produces 10 cwt. of carbon in the corn or fruit, 

 whereas the quantity of rain which falls upon an acre in four 

 months is only 700,000 lbs., wherein only 3cwts. of humic acid 

 can be dissolved, and applied to the purposes of vegetation. The 

 data are, however, all incorrect in this calculation. An acre of 

 sand without any coating of humus, yields frequently a produce 

 of scarcely 5 cwt., in which are only 2\ cwt. of carbon, and fre- 

 quently yields no harvest all ; the quantity of rain-water does not 

 determine* in the least the fertility of the soil, since a poor soil is 

 soon dried up after a quantity of rain, and a rich bottom during a 

 long drought may keep itself moist by hygroscopic action ; besides 

 which, in every soil a quantity of moisture rises from beneath, 

 which keeps it damp ; the solubility, moreover, of humate of lime 

 in water is by no means a measure of the quantity of carbon con- 

 tained in it, as the greater part of the humus enters the plant as 

 humous extract and perhumate of ammonia, which is very soluble 

 in water. 



Many persons have allowed themselves to be led astray by the 

 question as to the origin of carbon, inasmuch as they imagine that 



