INFLUENCE OF WATER UPON NUTRITION. 91 



State penetrate into these organs. It is for this reason 

 that cakes of rape seed, wild mustard, and nuts, used in 

 the manner mentioned above, afford the best manure 

 known. 



The waters constituting the third class, hold in solution 

 some salts ; these salts may be considered as performing 

 several offices in the act of vegetation; they stimulate the 

 vitality of plants, and increase the activity of their powers ; 

 they produce, in fact, upon plants, the same effects as those 

 produced upon the human body by the use of such condi- 

 ments as marine salt, and salt-petre. Salts of the same 

 nature as those contained in waters of the third class, al- 

 ways produce good effects upon the soil to which they are 

 applied, either by sprinkling the ground with them, or com- 

 bining them with barn-yard manure. 



Though these salts are useful to vegetation, it is neces- 

 sary to guard against using them in excessive portions, as 

 they then dry up and destroy the plants. Lands which 

 have been long overflowed by the sea, refuse to yield any 

 thing to cultivation till they have, by the repeated action of 

 fresh water, been freed from the salt with which they had 

 become impregnated. 



Some of the salts that are conveyed into plants by water, 

 exert an influence over them independent of their stimulat- 

 ing power ; being decomposed within their organs, and 

 serving, by the assimilation of their constituent principles, 

 as nourishment to the plants. The greater part of the salts 

 derived from the animal or vegetable kingdoms, are of this 

 description. 



Having considered water as a mechanical power, and as 

 a vehicle for the conveyance of food to plants, it remains 

 for me to make known its direct influence upon them. 



M. de Saussure has proved, by experiment, that plants 

 decompose water, and appropriate to their own uses the 

 hydrogen and the oxygen contained in it ; but this assimila- 

 tion is very trifling, if they cannot at the same time absorb 

 carbonic acid. The small increase of weight gained by a 

 plant in an atmosphere containing only oxygen, sufficiently 

 Terifies this. 



Dead plants which ferment when secluded from oxygen, 

 give out some carbonic acid ; but this only proves the 

 combination between the carbon and oxygen contained in 

 vegetable products. 



Next to carbon, the most abundant principle in plants is 



