Dear Sir - In your July number, I find a letter from that excellent western nomologist A. H. Ernst, of Cincinnati - commenting on Prof. Turner's discovery of insects, supposed to be the cause of blight in the pear, etc.

I had the pleasure of reading the Professor's June article, in his own house, at Jacksonville, and I also examined his apparently healthy remnants of a noble lot of pear trees, cut up by the blight of preceding summers. He could show me no vestiges of his " pear tree fiends," though he thought that their presence could be detected by a blotched and slightly diseased appearance of the foliage.

I would say, at the commencement, that I am skeptical on this subject of the insect origin of blight, and believe with Mr. Ernst that we are to look to the sudden and extreme changes of temperature, and perhaps other meteorological phenomena, for the immediate or exciting cause. But I do not believe that the enfeebled constitution of foreign trees is the only, or chief predisposing cause - for our native as well as foreign shrubs, and hardy indigeneous trees are subject to its attacks.

There is, as yet, no blight in my vicinity this summer, except in the burr oak ( Quercus macrocarpa) and it is due to the believers in the insect theory, that I state the fact of the comparative absence of most kinds of injurious insects in the orchard and garden - the scaly aphis excepted. We have had very few rose bugs even - not one where we formerly had one hundred. And this was the case during my recent visit to central Illinois.

There was, however, plenty of blight about Springfleld, and regions north, though none that I saw in Prof. Turner's neighborhood. I therefore fear that his exemption is accidental, rather than owing to his sealous manipulations and varied applications to the bark of his trees.

Professor T. deserves great credit, nevertheless, for his untiring exertions in this connection, and his very careful and expensive experiments. Profit to himself in this matter seems to be lost sight of, in his ardent determination to add something important to the science of Horticulture. And yet, Prof. Turner is a money making man. He will pardon me for this statement, because it is the best evidence that one can offer the world, of any man's practical talent, sanity, and sound orthodoxy. It is proof positive that he is all right, thought it has been the fashion among " the Doctors" in Illinois, to style the professor "a reckless innovator and a wild visionary "--especially in regard to " a plan for an Industrial University for Illinois" - for noticing which, as you have done, we of Suckerdom can never feel sufficiently grateful or thank you too much.

Now, whether Professor T. has made any new discovery in entomology or not, I cannot say - for I have never studied this most important science, and though I sought it, have not been able to procure a copy of Dr. Habbis' Treatise on Insects; I trust, however, that his new edition will be sufficiently large to enable western fruit growers, and the many reading farmers who have recently inquired for it, to obtain copies. But friend Ernst will permit me to assure him of one thing. Professor Turner's " mite of mould," which he presumes to be the nest of his "Pear Devil" is no! the "bark louse." The scaly insect does not attack the pear tree - at least net here - though the apple is often perfectly encrusted with these scabby little pests. The white scale insect is found on stunted apples and pears too, but I saw no signs of them on the trees about Jacksonville.

Still it Is possible that this insect and the nest seen by Prof. T. and Dr. Adams, are well known to entomologists - for though the one is a very learned man, and a most pa tient and persevering observer, and the other one of the best chemists in the west, and a man of great general scientific information - yet I am not aware that either makes pretension to an intimate knowledge of entomology - and I am compelled to doubt the deductions of Prof. T., while I admit them to be very plausible and even possible.

While writing (as my intended brief note has already grown to a letter,) permit me a word about your able Illinois correspondent, and the rich central Illinois region, which I do not remember that he has described, though he resides in its most favored spot.

Though an old correspondent I never met Prof. Turner before - and, as many of your readers may have done, I had formed no correct idea of the man. I had been told that he was a " hobby man," - "a visionary theorist," and all that sort of thing - and perhaps some of your readers may have thought the same, for he never hides his opinions; and their singular boldness, if not originalty, and his forcible manner of stating them, have startled his brethren, the school-men, and they are, consequently, more inclined to fear than to love him, though he has really made an hundred friends to one enemy; and if they would only read him right, and " the signs of the times" too, they would see in him as great a friend to relgious institutions, and polite letters, as to practical and scientific education.

J. B. Turner is a thoughtful man, but no " visionary" - an innovator - but no " level-er." He is not even an enthusiast - but an earnest scholar - a learned and pious theologian - strict in his example, and yet liberal in his views; and the most earnest and unselfish man I ever knew, in his desire to give the producing classes a liberal education, suited to their wants, and to the practical requirements of their several vocations.

I wish his detractors knew him as he is. I wish your readers could see his little place, and his manangement of it. His implements and machines, most of them of his own invention or improvement, and the manner in which he uses them - and how much he makes of, and how much he makes from, a few acres. They would then see that he is just the sort of a man to write for the Horticulturist, and the man to evolve and develop great practical thoughts, and to sustain them.

Jacksonville is the city, par excellence, of public edifices, and the great state charities. It is the classical town, and with many, the show town of Illinois; and it is a most lovely spot - though here, as elsewhere - "God made the country - man made the town".

The country is rich and beautiful, beyond the power of words to describe. The red drift, or diluvial soil, is astonishingly deep and productive, twenty successive crops of Indian corn, (60 to 80 bushels to the acre,) having been taken from the same field, without manure.

The face of the country is not broken, nor is it rolling, but just sufficintly sloping for easy culture, with an occasional elevation to break the vastness of a prairie view, which too often stretches away beyond sight, unrelieved by hills or trees.

Here, however, are some " mounds," and a plenty of timber, bordering the still streams, and clothing the range of elevated land which encircles the town, in the richest and most graceful dress imaginable.

We have no picturesque spots to speak of, and few trees of the picturesque type, though no country can surpass ours in the graceful school of trees, and in the gentle curves and swelling outline of much of our prairie land - its vastness and sameness being at once its principal beauty and defect. But about Jacksonville there is nothing like monotony - the landscape is varied, and the variety of trees and their forms, and the changing face of the general surface, are enough to prevent any idea of sameness.

Maples, Elms, and six noble sorts of Oak, make up the great mass of trees, and yet there are so many others, especially of the smaller sorts, that a prairie "island," or a " timber" border, resembles the show grounds of some old nurseries East, with specimens of nearly every beautiful and graceful deciduous shrub and tree.

But enough of the country - except the Hedges, and not much of them. There are hundreds of miles of new Maclura, or Osage Orange hedges, through the whole of this central Illinois region - and yet, I saw but one that would turn stock of all kinds, and that had grown up too rapidly, and not thick enough at bottom for future use. Prof. T. has some hedges commenced right - they turn chickens, and would almost turn a rat now - and hereafter they hid fair to he as impenetrable as a brick wall, and as formidable as a hedge of Cherokee rose, in Louisiana.

The great fault every where committed, is in not cutting back enough. The hedge looks dense and formidable at two or three years old, and the proprietors " hate to mu-tilate it." But they must cut and keep cutting, or they will never have a fence - that is clear to me - and yet, except upon Prof. Turnkr's grounds, I did not see ten hedges that had been half cut - nor three that had been cut enough. [Quite right - for the first three years the only thing is to cut down the hedge, till it gets thick at the bottom. Ed].

There were, as near as I can learn, about 30,000,000 of this hedge plant raised in Illinois, last season, and there will be perhaps fifty millions this - and these will make a "right smart chance of fence, if well planted and severely cut back - but I fear ten planters will curse the plant grower, where one will bless him; and all from their own neglect or folly - for I know that most dealers in hedge plants are very particular in their directions to " cut and keep on cutting." Almost every promising native or foreign plant has been tried for hedging and all abandoned, or nearly so, except the Osage Orange; and I fear the majority of the existing hedges of that will prove a failure, from the fact above stated, and not from any fault as yet discovered, in the nature of the plant itself, or in our soil or climate as regards its cultivation.

I noticed among trees that had been parts of a hedge once, the Honey Locust, ( Gledit-schia,) and in Prof. Turner's grounds are several tall specimens of the thornless variety - a half picturesque and very desirable tree. I did not see it with the moon-beams sifting through its feathery foliage, but the Professor described the sparkling shower of light thus produced, as most delicious, and entirely unequalled in its singular appearance. This variety should be oftener planted.

The architecture in Jacksonville, I ought to say before closing, is not of a high order. Many faults, and some bad ones, in the old public edifices - but better taste, and more knowledge, are shown in the new.

There are many new suburban cottages, a credit to the place. I asked the origin of so much taste, and was told that all might be traced directly to your Cottage Residences and the Horticulturist. A compliment to you, Mr. Editor, and well deserved. Truly your friend, John A. Kennicott.

The Grows,III, July 10,1852.