150 



Liquid Manure. 



plants flourish in it when watered with pure water only ; but every 

 difficulty was removed when he moistened it with the water from 

 a dunghill, for they then grew most luxuriantly; and M. Lampa- 

 dius still further demonstrated the powers of such a foul liquid 

 manure^ for he formed plots composed of only a single earth, pure 

 lime, pure alumina, pure silica., and planted in each different vege- 

 tables, watering them with the liquid drainings from a dunghill, 

 and he found that they all flourished equally well. The soluble 

 matters of a soil ever constitute, in fact, its most fertilizing portion ; 

 and if by any artificial means the richest mould is deprived of 

 these, as by repeated Avashings in cold or boiling water, the resi- 

 duum, or remaining solid matter is rendered nearly sterile : this 

 fact, first accurately demonstrated by M. Saussure,'^ I have since 

 confirmed by a variety of experiments of my own. 



The soluble matters or liquid manures consumed by plants are 

 sometimes imbibed by their roots unaltered, — in other cases they 

 are decomposed during their absorption. The earths, gypsum 

 and other salts, are instances of the first class; oil, and other 

 purely animal matters, of the last, Davy found that some plants 

 of mint which he forced to vegetate in sugar and water, appa- 

 rently absorbed the sugar unaltered, for they yielded a consi- 

 derably larger proportion of a sweetish vegetable extract than 

 those of the same weight which he had grown in common water ; 

 and it is an ascertained fact that the roots of plants will absorb 

 or reject the various earthy substances of a soil, or even when 

 placed in a saline solution, in a very remarkable manner ; thus, 

 when equal parts of gum and sugar were dissolved together in 

 water, and some perfect plants of polygonum persicaria placed 

 with their roots in the solution, it was found that they absorbed 

 thirty-six parts of the sugar, but only twenty -six of the gum ; and 

 when in precisely the same proportions and manner Glauber salt, 

 common salt, and acetate of lime were used, then it was found 

 that the roots of the persecaria separated these salts from the so- 

 lution with much ease, absorbing 6 parts of the Glauber salt, 

 10 parts of the common salt, but not a trace of the acetate of 

 lime.f 



These facts will not be uninteresting to the irrigators or occu- 

 piers of the English water-meadows, since they may in some 

 degree serve to account for the beneficial action of water on such 

 lands — a question not nearly so well understood as it ought to be, and 

 on which widely differing opinions are commonly held by practical 

 farmers. It is a theme intimately connected with the subject of 

 this paper, for irrigation is, in truth, a mode of applying the 

 weakest of liquid manures, on a very bold scale, to grass-lands. 



* Rech. 150. 



t Thomson, vol. iv. p. 321. 



