Mr. Editor : - I have received the August number of the Horticulturist, and through it, the answers to my questions, for which please receive my many thanks.

Well, Mr. Editor, I have "been and gone and done it;" that is, I have investigated the matter, and think I now understand my most worthy tutor.

There are undoubted, constant changes going on in the soil, although not apparent to sight or sound; we can sometimes use our olfactory nerves in detecting this change.

I now suppose that carbonic acid and ammonia are given off from the soil in any well constructed border in a green-house, or from the numerous small borders, alias pots of compost.

All good soils probably contain a considerable amount of carbon. If the soil containing this is properly drained of its superabundance of water, undoubtedly the air will enter the soil, and there work such wonders that we poor students never dared to dream of ever explaining to our entire satisfaction. One of these changes I suppose is, the oxygen of the atmosphere uniting with the carbon already in the soil, forming carbonic acid gas; probably part of this gas is absorbed by the rootlets, and part escapes into the atmosphere, there to be decomposed by the leaves, and stored in the plant as carbon. Am I right there?

But another point is, how does the air obtain any ammonia? If I remember rightly, the "doctors" tell us to never put undecomposed nitrogen into any border, and I can conceive in some manner how it would have a bad effect; if a chemical action is too great, in the presence of roots, it may have the power of killing them, as we know that the hydrogen of the air will speedily enter into nitrogen and decompose it, which action is very fast, sometimes producing a great amount of heat, as in the case of the common hot bed. And again, if nitrogen is to be supplied to the plant, it should be in the form of ammonia, and any compost containing this should have it so absorbed as to allow of no waste, i. e., volatilization; for, in open culture, all ammonia that we allow to escape into the atmosphere is so much lost to us.

But probably no compost has yet been prepared, with a sufficient quantity of ammonia in it, but that there were some portions of it that were not fully absorbed some would be escaping constantly from it for a long time. This would apply even with greater applicability to the green-house, as there the soil or compost is generally richer in ammonia.

Probably you mean that carbonic acid and ammonia are, generally speaking, constantly rising from the compost in a hot-house, thus supplying it to the confined air. Allowing a grape-vine in a pot to have three feet square of air, could it thrive if this air was not changed, or the portions that were absorbed by the leaves supplied; that is if the top of the vine was placed in an air-tight space of twenty-seven square feet, could it thrive? Does your humble student now understand you? A few words more, and then I shall quit this letter. Writing letters I am not used to.

I am glad to see that you combat the prevailing idea that trees and vines have larger roots, in proportion to their tops, in rich soil, than they have in poor soil. Page 387, Aug. No., "there are two quite distinct methods of making 'layers,' the one producing scarcely any thing but long roots, and the other a good system of fibres." Please tell us how, or the difference.

How can I obtain Harris's "New England Insects?" At what price? What works on vegetable physiology can you recommend me to study? where to get them, and price? Has Dr. Lindley ever published any works of this kind 1

[The above is one of the articles in the mislaid parcel of letters alluded to in our last issue. It has been a source of unmixed pleasure to have found it, for it happened to contain articles of much value. "Ventilation" has certainly got a very good idea of our meaning. His last article plainly discovered him to be a person of an intelligent and investigating turn of mind, and hence our replies to his queries were mainly suggestive. ' The wisdom of the course we took is now fully apparent. "Ventilation" is right The air in the green-house obtains ammonia not only in the way he supposes, from the earth, but the water used there in watering and syringing is richly charged with it, and from this source, not being fixed, it is constantly escaping. AH observant gardeners know that recently fallen rain water is peculiarly beneficial to plants; it is simply because of the abundance of ammonia it contains. A vine or plant placed in the conditions named will thrive until the space becomes too small for it; but it will not thrive as it would in a green-house, unless some means be taken to give motion to the particles of air.

We have had a number of applications in regard to our mode of making layers of the vine; but we purpose making a chapter of the subject in our "Hints on Grape Culture," and that chapter will soon be reached. Will you and others, therefore, have a little patience? It will need to be illustrated. Some publisher in Philadelphia undertook to get out a new edition of Harris on Insects, but we have not yet seen it. The old one can be purchased of Mr. Saxton. We do not know the price. We would advise you to read Wilson's Jussieu and Lind-ley. You can procure both through Mr. C. M. Saxton, of New York. We shall be glad to hear from you again. - Ed].