A. J. Downing, Esq. - Dear Sir: Your correspondent, Mr. Lewis F. Allen, in the March number of the Horticulturist, says " he would give a trifle to know if the old French Pear trees on the Detroit river were ever struck with the blight," and complains very justly, that cultivators in this quarter are so dilatory in giving the results of their experience. Being far more familiar with the horticultural implements than the pen, it is with some degree of diffidence that I say any thing on the subject, when there are so many, much more competent to do it justice.

In this vicinity there is nothing of the blight known, and we are told that " where ig-. norance is bliss, 'twere folly to be wise." The old Pear trees line the banks of the river for several miles, both above and below the city, and are still as healthy and vigorous as the native trees in the forest; and notwithstanding their immense size, being fifty or sixty. feet high, and from two to three feet in diameter, they are sound and solid to the heart, bearing regularly and well. One hundred and twenty bushels have been gathered from a single tree in a season. The fruit is not of the first quality, still it is very good, where there is little better to be had, and sells readily from four to six shillings per bushel. It more nearly resembles the Early Crawford, [Catherine? Ed.] than any other variety with which I am acquainted, and there is but very little difference in the quality of the fruit, among the old Pear trees around Detroit.

It is worthy of notice, that all the old and magnificent specimens of the pear tree, that have attracted so much attention among horticulturists, stand near the bank of the river, so that their situation is never wet, although the soil is very retentive of moisture, (being mostly a heavy black loam, from nine inches to a foot deep, with a stiff yellow clay subsoil.) Perhaps this' may be accounted for by the settlers at that early period, locating on the immediate banks of the river, which is evident from the shape of the farms, being only narrow strips, about eighty rods wide, and running back three miles, all considering it important to have a front on the river. By such an arrangement, each would have their fishing ground, and would also be better able to protect themselves from any incursion of the Indians.

Although the predominating soil is a stiff clay loam, still I have never seen so much diversity of soil in so short a distance, as there is to be found in the immediate vicinity of Detroit. At some period of the world's history, it was probably all submerged by the waters of the lakes.

I have grafted many of the leading varieties of the Pear on some of the old trees that stand on my place, and all seem to grow as vigorously as the original trees themselves; (they have not yet been grafted long enough to show specimens of the fruit,) vie: Onondaga, Angouleme, Bartlett, Virgalieu, Beurre Diel, Bloodgood, Ac. This brings to mind an anecdote that occurred in connexion with these pear trees. A Scotch friend came to visit me at the season when the fruit was at maturity. Wishing to test their qualities, he climbed the tree to assist himself, during which time he had been examing some of my labels, which were, perhaps, not very legible to him; when he came down he accosted me with - "queer peers," them; there is one marked the Vera Diel, an' anather Bloody-good, an' I couldna' read the rest." After a laugh, I told him that he had not read the names quite correctly.

I have noticed a disease in Pear trees brought from the east, which is, perhaps, the blight, and which may throw some light on the subject. When Pear, Peach, Apricot, Nectarine, and heart Cherry trees, are received in the fall, it is my invariable practice, to plant them away in a cellar till spring, thus preventing all possibility of their being winter killed; and this, too, would surely prevent the frozen sap blight. During summer the diseased specimens begin to show a yellowish, sickly appearance in the leaves; by degrees the tree is completely denuded of its foliage, black spots begin to exhibit themselves on the branches and trunk of the tree; finally the bark shrivels, vitality being longest retained immediately around the buds - this being the case sometimes, even throughout the winter, the roots and stocks being still apparently fresh. Is this the blight? I have never observed this disease after the trees have grown one season, without the aforesaid symptoms; may we not infer from this, that the malady was in the tree before it was received?

The winter with us, has been very severe - on the night of January 19, at 11 o'clock, my thermometer indicated 17° below zero. Many of the Bourbon and Remontant roses are killed down to the snow line. The beautiful new shrubs, Spirea prunifolia, and Wigelia rosea, have stood it bravely - not a particle of the wood is killed; this is certain-ly an excellent quality, as they are the most beautiful of the new shrubs that I have seen.

The Peach trees have also stood it well; the young wood was fully matured in the fall, so that not a particle of it is killed. In examining the fruit huds, I find that many of them exhibit the Mack speck in the heart; still they are not all killed, and if they are not more than half destroyed, it is rather beneficial than otherwise, as the tentendy of the Peach with us, is notoriously to over-bearing, and this saves thinning out.

Now this seems rather to combat your theory of the crop being destroyed when the thermometer reaches 12* below zero; under certain circumstances this may be the case, but that such is not the case under all circumstances, I am confident. During the winter of 1849, my thermometer indicated 18° below zero. This was shown by two different instruments, one of London, the other of Philadelphia manufacture; they hung side by side, so that there could be no mistake. Many prophecied that there would be no peaches next season; the season, however, showed a different result, for we were rewarded with an excellent crop. Respectfully yours, Wm. Adair.

Destroit. March, 1852