ORGANIZED BODIES. 
207 
All the nutriment which plants and animals require exists in the rocks, or has existed in 
them. Of these matters, silex, iron, lime and its various salts, magnesia, phosphates, etc. aro 
the most common, and these are generally distributed ; while arsenic, mercury or quicksilver, 
or rather their salts, which are poisons, are only found in very limited quantities, in veins. 
Now how is it that there is, apparently, a selection of food by plants 1 I may say, in answer to 
this question, that it arises from the structural differences of species. There are potash plants 
and lime plants; that is, some seem to require more potash, or lime, than others. This appa¬ 
rent selection of potash, or lime, is due, as already hinted, to the original constitution of the 
plant; in other words, it was made of such materials, and its elementary parts were so ar¬ 
ranged, that it is adapted to those special nutriments, and hence to take them up. This leads 
us to adopt the view that there is a speciality in the creation of beings, which extends itself to 
every species. The tobacco worm thrives upon this nauseous and poisonous weed ; who can 
doubt its special adaptation to it 7 for it is certain that it can not be ascribed to habit. How 
is it that marine plants live only where salt abounds 1 It is not because they have become 
habituated to it. There are many strong instances of this kind ; but wheat, rye and oats, 
though allied to each other, are equally special in their structure, by which speciality each one 
absorbs by its roots (because of their structure) more of the special element they require, than 
of others which they do not so fully demand.* 
Agriculture has not advanced yet far enough to enable us to adjust the amount of nutriment 
required by any crop. What agriculturists now aim at, and it is the most they can do, is to put 
within the reach of each plant all the nutritious elements its nature demands. These elements 
have been determined by analysis of the different pafts of plants; and very many of them may 
be found and consulted, in the second volume of the Agriculture of New-York. The elements 
of nutrition are not confined to the soil: the atmosphere is regarded by many as the great 
store house of carbon, the basis of vegetables. It has not been proved, however, that the car¬ 
bon of plants is derived solely from the atmosphere; and the fact that a great abundance of 
carbonic acid, and carbonaceous matters, is found in the soil, and enough to satisfy the wants 
of vegetation, is a fact in itself of sufficient importance to lead us to question the opinion that 
plants derive their carbon directly from the atmosphere. It is not enough to know that it is 
stored up in the atmosphere : its solubility in rain water rather indicates the mode by which 
it may pass into the vegetable tissues. Practically, it would be of little consequence to deter¬ 
mine the fact if plants derived their carbon wholly through the leaves ; for, as the amount of 
carbonic acid in the atmosphere is always the same, and the ability of plants to imbibe it can 
not be changed, they of course will take in their supply of this material, without cost or labor 
to the husbandman. In this view carbonaceous manures would lose some of their importance. 
If, on the other hand, plants derive their carbon from the soil, through the medium of the roots, 
* All that can be said is, that each species has its own organization, by which it lives its own and peculiar life; it 
is merely a statement of an ultimate fact. We may profitably ascertain, by observation, these peculiarities, by aid of 
the microscope. 
