derived from the atmosphere; but to say nothing of the argument which might be deduced from the advantage which is derived by plants from having their soil loosened about their roots, the experiments of Dumas and Boussingault prove that a tree which was cut off below the branches expired a large quantity of carbonic acid.  It may be asked how I know this was not precipitated by the rain.  I don’t know; but if the plant would assimilate this, why should it not assimilate that which arises from the decomposition of the carbonaceous matter in the soil?  My idea is that it does both, and that carbon in the soil does good if it offers an abundant supply of carbonic acid to the plant when it is in a condition to appropriate it.  Your allowance of lime appears to me to be far too small, for if any reliance can be placed on my experiments, lime can be profitably used to far greater extent than you seem to imagine.  And, again, you seem to think that where there is plenty of silex in the soil, the plant will be able to obtain as much as it requires.  I think that it is quite necessary that the silex should be in a soluble state, as I think that it is not only desirable that all the elements necessary to fertility should be in the soil, but that they should be in such a form that they can be assimilated by the plant.  Some of our compounds for producing fertility may perhaps be as absurd as it would be to give muriatic acid to a man troubled with indigestion, because free muriatic acid is found in the stomach of a healthy person.  Let me recommend you to try both silex and magnesia in a soluble state, and I think you will be satisfied with the benefit derived from their use.

Recurring again to the quantity of manure necessary to grow thirty-six bushels of wheat, I would ask, why limit yourself to so small a crop?  The difference in the cost of your manuring a field, and my manuring it, is more than made up by the increase of fourteen bushels of wheat and the corresponding increase of straw, even if the land did not improve every year by the application; and as the seed, rent, labour, and liabilities of the land are the same whether you grow a small crop or a large one, why not have it as large as possible?  Again, if I applied far more manure than was necessary, I ought to have had the crop equally good throughout the field; but on the ridge of the hill, where the soil was thin and poor, neither straw nor wheat were so good as they were where it was deeper and richer.  My own opinion is, that the plant is never able to extract from the soil all the manure, and therefore it ought to be brought up to a good standard before good crops can be expected.  I am not satisfied with any analogy that I can think of, but the best that occurs to me is that of a cloth in a dye-copper.  You can never get it to absorb either all or half the colouring matter, and if you don’t use far more than is taken up by the cloth, you will never obtain the desired results.  Besides, in chemical combinations it