102 ON THE FOOD OF PLANTS. 



vegetables, or by its deliquiescence it may in 

 some instances increase the fertility of the soil. 



Alkaline salts, no doubt, facilitate the solu- 

 tion of many animal and vegetable substances j 

 they also increase the divisibility, change the com- 

 bination, and otherwise exert an influence on the 

 soil itself, in a manner that adds tnuch to its 

 fertility ; indeed, there are many reasons for be- 

 lieving that alkaline salts increase the fertility 

 of soils, and the fertilizing powers of manures, 

 when mixed or combined with them : the 

 urine of cows, horses, &c., always contain a 

 portion of alkaline salts, and this is more fer- 

 tilizing than the dung of those animals. By 

 the reduction of vegetables by fire, alkaline salts 

 are produced •, and the action of fire on the 

 soil generally adds to its fertility : indeed, in a 

 great number of experiments, made with a view 

 to ascertain the most fertilizing, and the most 

 readily applicable and operative manure, or food 

 for plants ; I have found the serum, or the watery 

 part of blood, diluted with six or eight times its 

 bulk of water, and given to plants in the same 

 quantity, and in the same manner, as when 

 supplying them with water, once or twice only 

 in the year, to produce the most immediate, 

 and most fertiUzing effects of any thing j whilst 



