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< those parts of Russia that are under the same parallels of la
titude, probably does not differ very considerably; but in the • latter, the summers are exceedingly hot, and the winters in• tensely cold. In the spring, great degrees of heat suddenly o operate on plants which have been exposed to intense cold, ' in which excitability has been accumulating during a long
period of almost total inaction, and the progress of vegetation • is consequently extremely rapid.'..
These principles and facts are the grounds on which Mr Knight commenced his attempts to produce trees which should ripen their fruits earlier than usual. An apple tree was traine ed to a south wall, and the branches were in the winter dem tached and removed to as great a distance from it as their stems would admit, in order that the greatest quantity of excitability might accumulate by the inaction of the tree; and, in the succeeding spring, when the flower buds began to appear, the branches were again trained to the wall; the blossoms soon expanded, and produced fruit which early attained perfect maturity; and the seeds from their fruits afforded plants which, partaking of the quality of the parent, ripened their fiuit very considerably earlier than other trees raised at the same time fiom seeds of the same fruit which had grown in the orchard: this, of course, must be considered as a confirmation of the truth of Mr Knight's theory. Nearly every plant, the existence of which is not confined to a single summer, admits of two modes of propagatior, viz. by division of its plants, and by seed. By the first, an individual plant is divided into many, each of which, in its leaves, its flowers and fruit, permanently retains, in every respect, the character of the original stock; no new life is generated; and the graft, the layer, and cutting, appear to possess, in a great degree, the youth and vigour, age or debility, of the plant of which they once formed a part. No permanent improvement, therefore, can be derived from a graft or cutting which is but a continuation of the parent tree. On the contrary, seedling plants of every cultivated species sport in end.. less variety; and it is by a selection from these only, that new and improved varieties of each species of plant or fruit can be looked to.
II. The progressive influence of decay upon old varieties of fruit-trees is now admitted ; and the general law of Nature seems to be, that no living organized substance shell exist beyond a limited term. The diseased appearance of young grafted trees, particularly of the golden pippin, strongly confirms this position, although we are not willing to suppose that, like the supplemental noses of Taliacotius, the grafts are
to drop off the stocks on the death of the parent tree. All reasoning from analogy, however, confirms us in the opinion, that it is impossible to continue, by grafts or buds, any variety ad infinitum. Mr Knight is a strenuous advocate for this hypothesis: though we think there are some points of considerable difficulty to be got over. There are many well known varieties of trees which have been cultivated in this country for a very considerable time, such as the rose, the elm, &c. without any apparent loss of vigour. These, we however are aware, are propagated by an extension of the root; and this fact Mr Knight seems to consider as likely to insure grafts a longer continuance of vigorous existence. Mr Williamson, in a paper now before us, has in some degree controverted this position, that the cause of the diseased appearance of young grafted trees arises solely from the grafts being taken from old and decayed stocks. He states that, in the course of a few years, several young trees, which had been raised from seed, began to exhibit the same diseases, and to be affected by them in a greater degree than many of our older varieties; and that it is therefore evident that old age was not the only cause of these appearances. Mr W. ascribes the premature decay to the supposed diminution of the warmth of our summers. As a confirmation of this, it is to be remarked, that the golden pippin, which with us has become a shy bearer, in France, where the climate is warm, is still considered as a very productive tree. Without entering farther into the discussion of ihe question, there can be no doubt of the fact, that several of the older varieties of our fruits have been gradually decaying ; and we owe principally to the scientific exertions of Mr Knight, the introduction of many new and excellent varieties, which supply the loss of the old; and, from the spirit which has arisen, every season will no doubt continue to increase our stock. Mr Knight's theory, he conceives, is confirmed by Columella, who seems to have known that a cutting of a bearing branch did not form a young tree; for, speaking of the cutting of the vineSemina (he says) optima habentur à lumbis, secunda ab humeris, tertia summâ in vite lecta, quæ celerrime comprehendunt, et sunt feraciora-sed et quam celerrime Senescunt.
The inuring plants of warmer climates to bear, without covering, the frosts, the ungenial springs, and cold summers of this country, is a subject of considerable importance to the horticulturist. Little hitherto has been done in this respect with trees, because in general the propagation has been effected by cuttings or layers from the parent plant, which have therefore, in a great measure, retained its original habits; and we are now probably growing in our gardens the identical Laurel introduced
by • Master Cole, a merchant at Hampstead,' some years before the year 1629, in which old Parkinson published his Pa. radisus terrestris.
Most of our present wall trees are merely continuations, by grafts, of trees raised in a warmer climate; and although it is not probable that either near London or Edinburgh the peach tree will ever be brought to bear fruit so perfect and so delicious as that which is ripened in warmer climates, much may · be expected from the production of new varieties, raised in the manner suggested by Mr Knight's experiments, to procure early fruiting apples, and which shall have the habit of enduring our rougher climate. It is probable, observes Sir Joseph Banks, that wheat, now our principal food, did not bring its seed to perfection in this country till hardened to it by repeated sowings; and though some spring wheat from Guzerat, which was sown by him, eared and blossomed with a healthy appearance, many ears were, when ripe, without corn, and few brought more than three or four grains to perfection. Some seeds of Zizania aqua. tica were sown in a pond: the first crop produced strong plants and ripe seeds, the produce of which, however, was in the next year weak, and not half the size of the parent plants; but in each succeeding year they grew stronger, and in a few years attained their full size. Thus a plant, at first scarcely able to bear the cold summer of England, in fourteen generations became as strong and as vigorous as our indigenous plants. .
III. The creation of hybrid or mule productions, from two plants of distinct species or varieties, by fecupdating the blossom of one with the farina of the other, is also one of the ingenious devices adopted by Mr Knight, in order to obtain varieties of fruit, partaking of the different qualities of the two parent plants. Mr Herbert (Vol. IV. Part 1.), as far as we can understand him, is persuaded that, by such intermixtures, new species may be created amongst vegetables, capable of continue ing a distinct race by the natural descent of an unadulterated progeny to an indefinite extent, and without reverting to the single form of either parent plant. It is impossible to conceive any thing more improbabłe than such a position; and we entirely concur with the opinion intimated on this point in the Botanical Register (Vol. III. p. 195.), that no truly hybrid • plant, under any circumstances, will continue an unadulterated descent through seeds, beyond a very limited number of degrees ; and that the less complete productions of this kind, such as take place between remarkable varieties of one species, revert to the single likeness of either one or the other parent, or assume new appear. ances in endless vicissitudes.'
titled to ascribe the discrepancy in this case to the circumstance now mentioned, because the difference was so very minute in the other stations where the points of observation coincided. That these latitudes, then, are as correct as observed latitudes can be, we may safely assume; but it is possible that they may differ from the true latitudes of the several stations. If this difference can be accounted for, the anomaly above alluded to will be satisfactorily explained.
The diminution of the force of gravitation from the Poles to the Equator, may be found by the difference of the lengths of pendulums oscillating in equal times at the Poles and at the Equator; or by the ratio of the squares of the number of vibrations in 24 hours, observed in different latitudes, with the same pendulum. The diminution indicated by the decrease observed to take place in the number of vibrations between any two given latitudes, must be the same, from whatever portions of the me ridian it is computed, unless it be affected by some irregular attraction. But it is found from observations at Unst, and each of the other stations in succession, that the diminution deduced from the arc between Unst and Portsoy, is less than that obtained from the arc between Unst and Leith; the number expressing the diminution being .0053639 in the former case, and .005480 in the latter. When Unst and Clifton are the two latitudes, the diminution is .0056340; Unst and Arbury Hill give .0054282, denoting an increase of gravitation; Unst and London give .0055510; and a still further decresse appears from comparing the observations at Unst and Dummuse, the diminution thus obtained being .0055262. Again, Porses and Dunnose give .0055920, being a greater diminution the the last mentioned. Clifton and Dunnose make it on SESIS which is smaller ; while Arbury Hill and Dunnesegera which is greater than any of the preceding:
From these statements we gather, that in sicureigis De Equator, the decrease of gravity is greater than ASIES DET the theory; and also, that at some of the stines disturbing force, proceeding probably from
the the materials in the neiglorhoodhas made ty in the diminntinn of