PRESENT THEORY AND PRACTICE OF MINERAL MANURES. 433 
subject of special manures has received so much attention of late; for 
which exertions he has been rewarded with the position of extra pro- 
fessor (professeur-administrateur ) in the Museum of Natural History in 
Paris, where he delivers a course of lectures annually, and subjects 
his theories to practice on an experimental farm at Vincennes, estab- 
lished by the Hmperor upon land adjoining the imperial farm. This 
farm oceupies a surface of three hectares,* divided into five parallel 
lots, each of which is subdivided into twenty-four parcels of land. The 
manures are made with chemically pure ingredients, representing the 
constituent minerals of plants. Operations were commenced here by 
Ville in 1860, the results of which constitute the theme of his yearly 
lectures in the museum. The principle at the basis of his experiments 
is to supply as nourishment for plants those principles or salts which, 
according to analysis, are a part of their composition, and therefore are 
necessary for them; and as the species of plants may be numbered by 
the thousand, the manure or mineral supply must vary accordingly. 
The rule of this modern school, headed by Liebig, Lawes, Voelcker, 
and Ville, is, therefore, to supply to the land more phosphate, more 
potassa, and more lime than the harvests remove from it; and, according 
to the statement of these analyses, to furnish those elements which 
roots need and absorb. The rationality of the theory which underlies 
this rule ought to recommend it to public favor. It is only necessary to 
know beforehand what mineral element a plant requires, and it would 
appear at first sight a very simple matter to have this question deter- 
mined. All our common crops of food for man or cattle have been 
analyzed by accurate and reliable chemists. Select one of these and 
adopt it as the standard. But in looking over the several analyses of 
any simple plant, made by different chemists, we do not find that uni- 
formity of results which is desirable to render them reliable as exact 
statements. The substances present are found to differ very consider- 
ably in their nature, as well as in amount, and we have learned that 
some of this difference is due to varieties of soil, some to differences in 
the manure, and some to changes of climate and season ; that is to say, 
to greater or less continuance of solar heat and varying amount of 
rain-fall. A plant is, to some extent, like an animal; if plenty of food 
is supplied it will take up more than it needs; and if there isa defi- 
ciency of one element it will take up another to supply the vacancy. 
Here, then, is a difficulty at the outset; how much of the quantity taken 
up is the proper sum for healthy existence, and how much is superfluity ; 
and, since the elements vary in their nature, as found in plants grown 
in two localities, we are considerably in the dark as to which is the 
necessary and which the complementary element. We need greater 
exactness, and this we shall not attain until each plant is considered an 
individual requiring a certain amount of soluble food for its growth and 
development; until, in fact, we treat it like an animal or man. Man re- 
quires, when of average weight, (140 pounds,) thirty ounces avoirdupois 
of solid food daily, one-fifth of which, at least, should be albuminous and 
four-fifths amylaceous; about sixty grains of salt,and four pints of 
fluid. Just such a formula is necessary for each species of plant, and in 
order to obtain it exactly we have, by experiments yet to be made, to 
determine the essential and the supplementary food of the species. We 
know that soda will replace potash, and that magnesia may replace 
lime, but we do not always know under what circumstances and how far 
these aliments best subserve the ends for which we grow.the species. 
* Hectare, 2.4711 acres. 
28 A 
