Oil the Food of Flanlx, 
535 
mixturo as the ash of a plant usually presents, and which perhaps, 
after all, would be unnecessary. A good approximation is suf- 
ficient. 
It may be proper to mention that the green parts of the garden 
turnips examined contained a very notable quantity of some 
nitrate. 
Now, it appears to me that, by proceeding in this manner, we 
may eventually lay the foundation of a rational system of agri- 
culture. If, for example, we were in possession of a set of 
analyses of sufficient completeness and extent, both of the proxi- 
mate organic and mineral constituents of all such substances, the 
proportion of water and other things ; this information, combined 
with a knowledge of the gross weight of such crops, raised on a 
given space of ground, would enable us so to manage matters that 
the nature of the food and the extent of its supply should be duly 
apportioned to each class of plants ; and that, instead of annually 
loading our lands with manures, frequently at a great expense, 
whose mode of operation we very little understand, and in which 
it may happen that those very substances wanted are deficient, 
while others, already redundant, are supplied in injurious excess, 
we shall be able to proceed in a more systematic manner, and 
give the kind and quantity of food required, and no more. The 
thousands of tons of refuse matter rejected every year by those 
who conduct our immense chemical works of different kinds, may, 
when these things come to be better understood, be applied to 
the production of such artificial manures ; and the farmer may 
hereafter be enabled most materially to increase the produce he 
raises from the soil, partly by the actual augmentation of yearly 
harvest, but chiefly by the avoidance of the then unnecessary 
fallows and rotation crops. 
The Action of Manures. 
In the foregoing pages an attempt has been made to convey 
some notion of the chief conditions required to be fulfilled in 
order that a plant may live and thrive. We have seen that the 
food required for the sustenance of vegetables is strictly inorganic, 
and confined to a very few bodies — carbonic acid, water, and 
ammonia : may we add, in some cases, nitric acid ? These, to- 
gether \vith saline matter derived from the soil, are the only sub- 
stances we know of required for the sustenance of plants, or 
indeed capable of ministering to their existence ; and once more 
it is well worthy of remark that these are the very substances pro- 
duced by the functions of animals during their life, and by the 
decay of their bodies after death. 
The science of agriculture will thus resolve itself into a know- 
