Possibly there may be readers of the Horticulturist not much acquainted with Mr. Kniogt's labors, and who may not, therefore, be able to appreciate the deference which is due to him as a patient, ingenious, and truth seeking inquirer. No one can better testify to his great merits than Dr. Lindley. In a memoir of Mr. Knight, published in the Atheneum, Dr. Lindley, when alluding to his celebrated paper on the inheritance of disease in fruit trees, and other communications laid before the Royal Society, said, "in all these researches the originality of the experiments was very remarkable, and the care with which the results were given, was so great, that the most captious of subsequent writers have admitted the accuracy of the facts produced by Mr. Knight, however much they may have differed from him in the conclusions which they drew from them. No man living, now before the world, can be said to rank with him in that particular branch of science to which his life was devoted."

One of the first subjects to which Mr. Knight's attention was directed, was the unhealthy condition of several old and famous varieties of the apple and pear; he was told by neighboring nurserymen that they could no longer raise healthy and profitable trees a vulgar error, and he commenced a series of experiments with the express view of proving it to be so. Instead, however, of holding an imaginary conversation with the old trees, after the fashion of your correspondent, Mr. Marshall, he allowed them to speak for themselves; he questioned and cross-questioned them, with an ingenuity and perseverance as trees were never questioned before, in the vain hope to shake their testimony and non-suit the nurserymen; but they told him plainly, repeatedly, and decisively, in a language not to be misunderstood, that their doom was sealed; that the vigor of youth, and the productiveness of mature age, had passed away; that they were no longer able to sustain their former labors, and nothing but increasing infirmities remained for them.

An account of his experiments in this matter, was the subject of his first communication to the Royal Society, in 1795, and in a communication to the Horticultural Society, in 1824, when his views had been subjected to much criticism and no small amount of ridicule, he stated that, "every experiment which seemed to afford the slightest prospect of success, was tried by himself and others, to propagate the old varieties of apple and pear, which formerly constituted the orchards of Herefordshire, without a single healthy or efficient tree having been obtained;" and what Andrew Knight, and other practical men, found by repeated experiments to be impracticable, no man, that I am aware of, has yet proved by experiments in the climate of England, to be feasible; and that, I apprehend, is an important fact which should not be altogether lost sight of in this inquiry.

"Of the apples mentioned and described by Parkinson," Mr. Knight says, "the names only remain; but many of Evelyn's are still well known, particularly the Red-streak; we had many trees of it, but they appear to have been in a state of decay during the last forty years; others mentioned by him are in a much better state of vegetation, but they have all ceased to deserve the attention of the planter."Dr. Lindley does not attempt to deny these facts, but offers what we may presume he considers to be a more satisfactory explanation. Besides the main point at issue, three foolish propositions are gravely examined in these anticles, and as a matter of course, are very cleverly proved to be untenable. They are these: 1. It is alleged that seeds renew the languid vigor of a species as often as they are sown, and that if an unhealthy plant is multiplied by seeds, the immediate offspring becomes healthy. 2. It is also said that multiplication by seed is the only natural mode of propagation known among plants. 3. Seeds are said in all instances to produce healthy plants, but this, as Lindley truly observes, "like the previous assertions, will not bear exact investigation."As, besides Mr. Knight, no other writer is referred to but myself, in these articles, I may, in case any readers of the Horticulturist should have access to the Gardeners' Chronicle, be allowed in self-defence to say, that these propositions did not emanate from me.

Dr. Lindley, in attempting to disprove the soundness of Mr. Knight's views, goes at once to the root of the matter, by boldly denying that vegetable, like animal life, has its fixed periods of duration: he says, "trees, and other wild perennial plants, have never yet been shown by any trustworthy evidence to be subject to decripitude arising from old age. On the contrary, every new animal growth is a renewal of their vitality. In the absence of disturbing causes from without, there is no intelligible reason why a forest tree should not continue to grow to eternity." If there be, indeed, no trustworthy evidence on record showing that trees become decrepid through ags, the only conclusion that I their course in a few hours or days, the life of others extends beyond a century, but the end of all is death. So of plants: some spring into existence, fructify and die within a week; the life of others is limited to five or six months; and so the period of existence gradually extends until we come to the monarchs of the forest, which may boast of a life of one thousand years and upwards.

But because they have lived so long, are we then to conclude that there is no limit to their existence, that they form an exception to all other organic beings, and that they can never suffer decay through the infirmities of age? Most assuredly not. A more unwise or inconsistent supposition never entered into the mind of man. The lordly oak labors under the same irrevocable decree as the humble weed. - dust they are, and unto dust they must return.

As a set off to Knight's experiments on the apple and pear, some instances are cited by Dr. Lindley, of cultivated plants having been propagated by division a considerable time, without wearing out. The white buttery pears of France are said to have been propagated by division, from time immemorial, and exhibit no trace of debility. I am not acquainted with the history of the white buttery pears of France, and cannot, therefore, say what value is due to this statement. I may observe, however, that it is anything but satisfactory or conclusive evidence. French writers might with equal truth say that white heart cherries, or pink-eyed potatoes, had been cultivated in England from time immemorial. There are, and have been, however, many varieties of these plants known by these names; and as the duration of the pear is supposed to be somewhere about four hundred years, possibly this period, even supposing one variety only has been known to French writers under that name, is amply sufficient to constitute a "time immemorial." My desire, however, is to arrive at the truth, and if your knowledge of fruits, Mr. Editor, will enable you to confirm the accuracy of Lindley's statement, let him have the benefit of your knowledge.

Dr. Lindley further remarks, that "some vines which are supposed to have been in existence, in the days of Columella, have been transmitted by division to the present day." The fact that varieties of the vine had been propagated by cuttings a considerable time, was the chief reason advanced many years ago by Loudon, to prove that Mr. Knight's views were erroneous, and when I considered the spirit in which the objections seemed to have been penned, and the extent of Loudon's knowledge of garden history, it tended in no small degree, to convince me that truth was on the side of Mr. Knight; for even supposing the conjecture is true, that some vines of the present day are the same varieties mentioned by Columella, surely an impartial inquirer after truth, must be ready to confess that this seemingly formidable objection is, in reality, no objection whatever, seeing that the vine is one of the longest lived plants known; nay, so long will individual plants of the vine live, that Loudon says, "the age which the vine will attain in warm climates, is so great as not to be known; it is supposed to equal or surpass the oak." If this be so, then there is obviously nothing improbable in the supposition that a plant of the vine living in the days of Columella might, if not destroyed by violence be living now; it is, therefore, perfectly consistent, with Mr. Knight's hypothesis, that varieties of the vine mentioned by Columella, may have been continued by division to the present day.

And yet because varieties of this long lived plant have been propagated by cuttings during centuries, we are required to believe that varieties of the potato, and other short* lived plants, propagated in like manner, do not wear out and become feeble in consequence of age, but that with due care, they may be made to live forever!* John Townley.