READERs of the Horticulturist, and especially the numerous admirers of Mr. Downing, must have rejoiced to see an advertisement in the late numbers, announcing a new edition, under the auspices of his friend and literary executor, Henry W. Sargent, Esq., of Wo-denethe. No other person that we know in this union, is so well qualified for the task of bringing the work up to the present day. It must afford pleasure to all lovers of rural art, that Mr. Sargent has consented thus to aid the dissemination of correct taste, and we feel very sure that to no other person would Mr. Downing have so willingly consigned this duty of respect and love. In the enumeration of new trees it will be complete, and in each department the notes of our friend will add much to the value of the publication. It will not be issued before next spring.

Mr. Sargent requests, in the advertisement, that our readers will afford him any information they may possess respecting the character or hardihood of any of the newer evergreen or deciduous trees, which have been introduced into cultivation within the past ten years, as he is desirous of comparing the varied success of the same tree in the different portions of the United States. All who have this kind of information, will of course, most cheerfully contribute their portion to so desirable a comparison.

Some time since, we published a few "Familiar Letters," from Mr. Downing which had been preserved in a file we chanced to be looking over. They exhibited the man in his private character, when not dressed up, if one may use the expression, in his party apparel. They were simple expositions of the excellence of his head and heart - mere commonplaces between one friend and another - and yet they met with a response in every quarter, and correspondents frequently ask for more. In the following, which we have but just discovered, Mr. Downing speaks gracefully and modestly of his professional engagements, and numerous calls on his time; there is no affectation of great success - he is preparing descriptive lists of fruit for the catalogue of the nursery, "which cost me a great deal of labor," - is grateful for a few criticisms - rejoices calmly that some of "my castles in air" will soon be brought into palpable form, and recapitulates with pride Miss Sedgwick's plan of advertising her copy to lend. "I wish," he says so naturally, and so beautifully, "the little volume were perfect, to deserve the friends it has made".

This letter was written almost five years before the commencement of the Horticulturist, when his fame was less extensively disseminated than afterwards, and when he was just beginning to feel his own powers; he was then engaged in the nursery business, which was soon abandoned for the pen; a happy combination of early practical knowledge, with aspirations after the true and beautiful, which so eminently made their mark upon the public taste, as for long periods to constitute an era of even historical interest.

"We never tire of hearing about Downing," writes the most agreeable of lady correspondents from the west; "pray tell us all that can be known." We can do this in no better mode than to let him speak for himself, and in presenting the following previously unpublished letter, we believe we are occupying a little space advantageously and agreeably. We will only add that if any of our readers possess relics of the kind, it will confer a public favor if they will consign copies to our hands.

Newburgh, 21st Oct., 1842. J. Jay Smith, Esq., Philadelphia, Penn.

My dear Friend: - I have just returned from Boston, after a considerable absence from home, this morning; and your letter strikes with such an iron tongue upon my heart, that I sit down at once to reply to it. I assure you my silence has been as unwished for on my part, as it could possibly have been on yours. But 1 have never had so absorbing a season as I have since you left me - having been thoroughly driven with business matters - persons occupying my time here, or landscape gardening journeys abroad, constantly; and whenever I have had time to write, I have been driven to write numberless professional letters, always awaiting me when I come home; and putting off those two or three correspondents nearer my heart, because I felt that they could pardon my temporary silence. And I have many times reproached myself that I have not before answered the very kind letters and notices from you and others which I have found awaiting me at different times.

I have been lately employed at the state lunatic asylum at Utica, a magnificent new establishment, to design the grounds - at private places at Boston, Albany, New Haven, Long Island, Staten Island, two places in New Jersey, etc, so that you see my art is flourishing.

1 am now home for the season, our busy autumnal trade now commencing. Besides this, a good deal of the time I could catch has been employed in preparing the descriptive lists of fruit in our new catalogue, which cost me a great deal of labor, and which I am sure will be found valuable by all interested in fruit.

I have your unanswered letters all before me, and am greatly obliged to you for the kind opinion you have formed of my "Cottages." The criticisms I have also noted for use, in a new edition, with improvements, which I trust may come before a long while, as the work has been very favorably received. Some of my " castles in air" I have the satisfaction of knowing will be soon brought into palpable form by amateurs in different parts of the country. No. 2 is an especial favorite, and I have just now a letter from a gentleman unknown to me, at Charleston, who writes to know where, and at what price he can buy a place of a few acres, on the North river, to build this cottage upon! My friend, Miss Sedgwick, has written me a letter, in which she enters heartily into our feeling of the subject, and says she means to advertise her copy to lend, in the Stockbridge paper, to any of the farmers. I wish the little volume were perfect, to deserve the friends it has made; but I shall be gratified if it does its part towards rousing our good people in matters of architectural taste.

The booksellers all say that now something of a more simple character is wanted, on farm buildings, etc.

I hope your health, which I hear has been so poor, is now well recovered. It would have given Mrs. D. and myself great pleasure to have been with you again in September, but we could not achieve it, as my engagements and the guests she was receiving at home, put it out of our power, unfortunately. I especially wanted to send something to your horticultural fair, but was detained in the North a day or two too late; next season I must try to do better, and be more systematic in my arrangements.

Some few things you want we have not for sale, as the Virgilia lutea, but I will make it up in other things, and will take care of you in due time.

1 see there is to be a plate of Ashland in a popular life of Clay, in press; perhaps it will furnish something for my use in the edition of the L. G. for which I am preparing new material for this winter; and in which task I shall at all times be most truly glad to have hints from you.

Mrs. Downing begs me to present her kindest remembrances to you, and we both join in kind regards. Next summer we hope - will join you in a visit to the Hudson Highlands, and you shall be made more thoroughly familiar with the merits of the North river than you were this season.

I was also in debt to our friend Mr. Notman, who wrote me a very kind letter, which I will soon answer in extenso. We have a great acquisition in Mr. Upjohn, the architect of Trinity Church, N. Y., (which is really growing more exquisite every day,) a church which will stand as far before all other Gothic structures of the kind in this country, as a Raphael's Madonna before a tolerable sign painting. Mr. U. has in progress also, some noble and artistic alterations or improvements on the old manor house of the Van Rensselaers, at Albany, which I have inspected, and like greatly. You may judge of the effect of the whole, when 1 tell you that these alterations alone cost $30,000, and this on a house nearly 90 years old. Still very fine. The hall 50 by 25 feet.

I can now promise to answer you more faithfully, so pray overlook my apparent neglect with your accustomed generosity, and write soon to yours, very sincerely, * A. J. Downing.