The Mineral Theory. 
505 
phuric acid, lime, magnesia, potash, iron ; and many, too, require common 
salt." 
As I did not admit the existence of organic food, my theory 
was called mineral theory. This name was correct, inasmuch as 
it was directly opposite to another theory, which prevailed before 
1840. 
According to De Saussure, Sprengel, Thaer, &c, there were 
two different laws of nourishment, and two kinds of manure, organic 
and inorganic. 
" Uncultivated plants," says Dc Sanssurc, " receive their combustible elements 
from the air, their carbon from carbonic acid ; but the products generated from 
this kind of food possess no value for agricultural purposes. The normal 
development of cultivated plants, on the other hand, and the amount of pro- 
duce of arable fields, depends on organic matter in the soil, on residues of 
fermentation, and decay of animal and vegetable matter." 
"Fertile soils contain a mixture of these remains, and their absorption by 
the roots is a powerful assistance to the food which is contributed by the air 
and water." 
" Plants receive their nitrogen almost entirely by the absorption of the 
soluble organic substances." 
" Mineral substances, marl, gypsum, clay, lime, favour the growth of plants, 
but take no part in nourishment." — (See ' Bibliotheque Uni verselle,' t. 3, p. 430 ; 
' Ann. of Chemistry,' t. 42, p. 235.) 
This view, it will be seen, is diametrically opposed to my 
theory, inasmuch as De Saussure maintained the necessity of 
organic food for cultivated plants, and I denied it altogether. 
At first sight the so-called theory of Lawes, or his definition of 
manure, would seem exactly identical with that of De Saussure. 
Mr. Lawes assumes the existence of different laws for cultivated 
and uncultivated plants, and of two classes of manure, organic and 
inorganic, just as De Saussure and Sprengel maintained ; Mr. 
Lawes does not claim this theory as his own, but states that it 
was generally understood, though by no means satisfactory. 
There are, however, two essential differences between Mr. 
Lawes's so-called theory and that of De Saussure. First, that 
Mr. Lawes admits the existence of inorganic food or manure, 
consisting of the substances contained in the ashes of plants. 
The second, that Mr. Lawes applied the name of organic manure 
to something very different from what De Saussure meant. For 
the first, De Saussure knew nothing of the fact that the ashes of 
plants were nutritive elements ; for he maintained that they (for 
instance, potash, lime, magnesia), were variable ingredients, 
changing with the geological formation and character of soils. 
I think no one can deny that I was the first to point out that the 
elements of the ashes were really food of plants, and Mr. Lawes 
has most certainly no claim to this essential part of my theory. 
As to the second, by organic manure De Saussure meant 
