CHEMISTRY IN AGRICULTURE AND PHYSIOLOGY. 561 
plants constantly, and therefore must be looked upon as 
natural constituents, is very inconsiderable, viz.:—1 oxygen, 
2 carbon, 3 hydrogen, 4 nitrogen, 5 sulphur, 6 phosphorus, 
7 chlorine, 8 potassium, 9 sodium, 10 magnesium, 11 silicium, 
12 iron. 
Eight of these elementary substances must be present in 
the soil it plants are to flourish luxuriantly ; these eight sub¬ 
stances are like eight links of a chain round a wheel. If 
one is weak, the chain is soon broken, and the missing link 
is always the most important, without which the machine 
cannot be put in motion by the wheels ; the strength of the 
chain depends upon the weakest of the links. 
The principal mass of all vegetable substances is composed 
of oxygen, carbon, and hydrogen; these furnish the materials 
for the formation of the cell-membrane, and nitrogen is an 
essential constituent of the proteine substances, as albumen, &c. 
Sulphur and phosphorus, although contained in inconsiderable 
quantities in plants, play an important part, being necessary 
constituents for the formation of the proteine compound. 
And here it may be well to state more fully the important 
fact, that plants are formed from these materials, only when 
the atmosphere and soil supply them at the same time in 
suitable quantity and in proper proportions ; the four “at¬ 
mospheric elements,” oxygen, carbon,hydrogen, and nitrogen, 
do not nourish without the simultaneous action of the ele¬ 
ments of the soil, and the latter are equally valueless without 
the former. It hence follows, as a matter of course, that no 
single element of plants named above possesses superiority 
over another. 
Of all the elementary substances which enter into plants 
oxygen is the only one that is taken up in a pure condition; 
plants can only appropriate the others out of chemical com¬ 
pounds, which for the most part they decompose. Here at 
once arises the question, whether the elementary substances, 
when they are to serve as food for plants, must be already 
combined with organic compounds, or whether plants possess 
the power of feeding upon inorganic compounds ? In no 
question of vegetable physiology has so active a strife existed 
as on this, especially since Liebig appeared as a defender 
of one of the extreme answers to it. 
Although no universally valid answer can be given to this 
question, it is beyond any doubt that plants, if not as a 
whole, yet in an overwhelming majority, possess the power 
of forming organic out of inorganic substances, and that 
inorganic substances mostly play the principal part in 
nutrition. This is evident both from observations made 
