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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
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 the 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 summie in vite lecta, quæ celerrime comprehendunt, et sunt feruciora-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 Paradisus 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 kabit 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 aquatica were sown in a pond : the first crop produced strong plants and ripe sceds, 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 fecundating 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 continuing 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 improbable 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 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.'
Several hybrid apple trees, the produce of the Siberian crab, and the richest of our apples, have been the result of Mr Knight's experiments; and which, while partaking of the hardiness of the Siberian crab, and ripening in cold and exposed situations, yet possess the fine qualities of the other parent. In some, the varieties inherit the character of the male, and 0thers of the female parent, in the greatest degree; and from some varieties of fruit, particularly the golden pippin, a better copy was obtained by introducing the farina into the blossom of another apple, than by sowing the seed of it. The excellent variety called the Downton pippin, was obtained from the farina of the Golden, and the female flower of the Orange pippin.
We extract from the Pomona Herefordicnsis the account given by Mr Knight of the course he adopted in his experiments.
• Prepåratory to these experiments, many varieties of the apple were collected, which had been proved to afford, in mixture with each other, the finest ciders. A tree of each was then obtained, by grafting upon a Paradise stock; and these trees were trained to a south wall, or, if a Siberian crab, to a west wall, till they afforded blossoms; and the soil in which they were planted was made of the most rich and favourable kind. Each blossom of this species of fruit contains about twenty chives or males, and generally five pointals or females, which spring from the centre of the cup or cavily of the blossom. The males stand in circle, just within the bases of the petals or flower leaves, and are formed of slender threads, each of which terminates in a small yellow ball or anther. It is necessary in these experiments, that both the fruit and seed should attain as large a size, and as much perfection, as possible ; and therefore a few blossoms only were suffered to remain upon each tree, from which it was intended to obtain seed. As soon as the blossoms were nearly full grown, every male in each was carefully extracted-proper care being taken not to injure the pointals or females; and the blossoms, thus prepared, were closed again, and suffered to remain till they opened spontaneously. The blossoms of the tree which it was proposed to make the male parent of the future variety, were accelerated by being brought into contact with the wall, or retarded by being detached from it, so that those were made to unfold at the required period; and a portion of their poilen or farina, when ready to fall from the mature anthers, was, during three or four successive mornings, deposited upon the pointals of the blossoms, which, consequently, afforded seed. It is necessary, in this experiment, that one variety of apple only should bear in unmutilated blossoms; for, where other varieties are in flower at the same time, the pollen of these will often be conveyed by the bees to the prepared blossoms ; and the result of the experiment will, in consequence, be uncertain and unsatisfactory.
• Every seeds though many be taken from a single apple, will af:
ford a new and distinct variety, which will generally be found to bear some resemblance to each of its parents. Examples of this are presented in the Grange apple and Downton pippin, and in the Foxley apple and Siberian Harvey. ..,
? After varieties are thus formed, the operator has still to wait long before he can estimate the success of his labours. A seedling pear tree does not often bear fruit till it is ten, and sometimes not till it is sixteen or eighteen years old ; but å seedling apple tree will generally produce fruit at six or seven years old, and sometimes even at four, when either of its parents has been the Siberian Crab. The success of the experiment is also still uncertain : many of the new varieties will be worthless; and where the fruits are good, the trees will often prove unproductive, or defective in health and vigour; and the planter must think himself fortunate if, under the best management, fifty seeds afford a single fine variety for the press; though many will probably be above mediocrity.'
IV. Experience shows that the different varieties of vegetables, when long propagated, gradually lose some of the good qualities which they possessed in their earlier stages of existence. About fourteen years, it seems, is allotted to the duration of a variety in a state of perfection; and Mr Knight has applied the principles before noticed to the production of new and early varieties of the potatoe. Observing that those varieties which were early, produced little blossom and no seed, he conceived this to arise from the nutriment being chiefly carried away to supply the tuberous roots (or potatoe) which are produced on runners, and are distinct from the fibrous roots. By destroying the runners, and only permitting the fibrous roots to grow, early blossom and perfect fruit was procured; from which new varieties were obtained, which in a great degree inherited the early habit thus given to the parent plant.
:?,. .? The trouble and the uncertainty, and the length of time which it was supposed was necessary for the production of varieties from seed, are the principal reasons why, so little has hitherto been done: but considerable error and prejudice has existed on this subject. In New South Wales, a Peach tree (which arrives at puberty earlier than any other fruit) is said to have borne at the end of sixteen months from the planting of the stone. In America, whole orchards of peaches are used for making brandy and feeding hogs ; and these are always planted from the stone, and bear at the end of the third year. And a peach stone planted by Mr Knight in the middle of February, kept under glass, and frequently supplied with fresh manure, had, in the following autumn, formed blossom buds, capable, as he conceived, of bearing fruit.
V. The construction and form of forcing-houses is an object of considerable importance, and hitherto appears to have beeni very defective; and two are rarely built alike, though intended for the same purposes. The object is to procure a building in which the greatest possible quantity of space has been obtainedly and of light and heat admitted, in proportion to the capital expended.
The introduction of steam, in metal pipes, for the purpose of warming forcing-houses, instead of thick brick flues, and the improvement in the form, which admit of the ripening more fruit in a house built at a smaller price, render it probable that they will become much more common, and that larger ones will be built, in which the tropical fruits may be ripened with facility; more especially as a greater and more regularly continued degree of heat may be furnished by steam at a comparatively trifling expense. Already the fruit of the Grenadilla, the Loquat, and the Mango, have been ripened in this country; and it is probable that, at no very distant period, the Aki, the Avocado pear, the Flat Peach, the Mandarine Orange, the Litchi of China, the Mangosteen, and the Durion of the East Indies, and other valuable fruits, will add to the luxury of the tables of the rich. One year in three has already been saved in the time of fruiting the Pine,—and the necessity of the use of tan in its cultivation in a great measure done away with, as stated by the President; and we are led to suppose that the time is at no great distance, when this expensive fruit will be no longer an object of rarity, from the cost of its cultivation.
Considerable difference of opinion exists as to the best form of a forcing-house. It is however evident, that when fruit is to be ripened in the same climate and season of the year, one peculiar form must be superior to every other; and that in our climate, where sunshine and natural heat do not abound, the form which admits of the greatest quantity of light through the least breadth of glass, and which affords the greatest regular heat with the least expenditure of fuel, must generally be the best. The sun, of course, operates most powerfully on the force ing-house, when its rays fall most perpendicularly on the roof; because the quantity of light that glances off without entering the house, is proportionate to the degree of obliquity with which it strikes upon the surface of the glass. Mr Knight conceives the best elevation for latitude 52, to be that of about 34 degrees.
Hothouses are comparatively of modern introduction, and were probably little, if at all used in this country, in the beginning of the last century. Lady Wortley Montagu observes, on the circumstance of pine apples being served up in the des