Sidebilder
PDF
ePub
[ocr errors]

around which they are arranged has itself no tendency to elongate under the influence of the usual stimulants. Hence, a flower bud, or flower, is nothing but a contracted branch; as is proved by the occasional elongation of the axis in flowers that expand during unusually hot damp weather late in the spring, becoming branches, bearing sepals and petals instead of leaves. It is, therefore, easily to be understood why, so long as all the motions in the fluids and secretions of a tree go on rapidly, with vigour, and without interruption, only rudiments of branches (or leaf buds) should be formed ; and why, on the other hand, when the former become languid, and the parts are formed slowly, bodies of a contracted nature, with no disposition to extension, (or flower buds,) should appear.

. It will be found that the success of the practices above enumerated, to which the gardener has recourse in order to increase the fertility of his fruit trees, is to be explained by what has just been said. In ringing fruit trees, a cylinder of bark is cut from the branch, by which means the return of the elaborated juices from the leaves down the bark is cut off, and all that would have been expended below the annular incision is confined to the branch above it. This produces an accumulation of proper juice; and flower buds, or fertility, are the result. But there is a defect in this practice, to which want of success in many cases is no doubt to be attributed. Although the returning fluid is found to accumulate above the annular incision, yet the ascending sap flows along the alburnum into the buds with nearly as much rapidity as ever, so that the accumulation is but imperfectly produced. On this account the second practice, of bending branches downwards, is found to be attended with more certain consequences. The effect of turning the branches of a tree from their natural position to a pendulous or a horizontal one is, to im

a

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small]

pede both the ascent and the descent of the fluids in a gradual but certain manner. The tissue of which branches are composed is certainly permeable to fluids in every direction; and there can be no doubt that the vital action of the vessels of a plant is performed both in the natural and in an inverted position. So long as that erect direction of the branches which is natural to them is exactly maintained, the flow of their fluids, being subject to no interruptions, will take place in the freest possible manner ; but the moment this natural direction is deviated from, the vessels become more or less compressed, their action is impeded, and finally, if the inversion is perfect, it becomes so slow that an accumulation of the proper juices necessarily takes place through every part of the system.

One of the objects of training is to produce the same effect. Branches are bent more or less from their naturally erect position; their motion, in consequence of the action of winds upon them, which is known to facilitate the movement of the fluids, is totally destroyed; and hence arises the accumulation of proper juice which is necessary to their fertility. Nor is the influence of the stock of an essentially different nature. In proportion as the scion and the stock approach each other closely in constitution, the less effect is produced by the latter ; and, on the contrary, in proportion to the constitutional difference between the stock and the scion, is the effect of the former important. Thus, when Pears are grafted or budded on the wild species, Apples upon Crabs, Plums upon Plums, and Peaches upon Peaches or Almonds, the scion is, in regard to fertility, exactly in the same state as if it had not been grafted at all. While, on the other hand, a great increase of fertility is the result of grafting Pears upon Quinces, Peaches upon Plums, Apples upon Whitethorn, and the like. In these latter cases, the food absorbed from the earth

[blocks in formation]

the ind Che ural

mer.

by the root of the stock is communicated slowly and unwillingly to the scion ; under no circumstances is the communication between the one and the other as free and perfect as if their natures had been more nearly the same ; the sap is impeded in its ascent, and the proper juices are impeded in their descent, whence arises that accumulation of secretion which is sure to be attended by increased fertility. No other influence than this can be exercised by the scion upon the stock. Those who fancy that the contrary takes place ; that the Quince, for instance, communicates some portion of its austerity to the Pear, can scarcely have considered the question physiologically, or they would have seen that the whole of the food communicated from the alburnum of the Quince to that of the Pear is in nearly the same state as when it entered the roots of the for

Whatever elaboration it undergoes must necessarily take place in the foliage of the Pear ; where, far from the influence of the Quince, secretions natural to the variety go on with no more interruption than if the Quince formed no part of the system of the individual.

If we consider upon what principle the flavour of particular fruits may be improved, we shall find that it is entirely due to the increased action of the vital functions of leaves. When the sap is first communicated by the stem to the leaves, it has experienced but few chemical changes since it first entered the roots. Such changes as it has undergone have been due rather to the solution of some of the pre-existing peculiar secretions of the individual by the sap in its way upwards through the alburnum, than to any other cause. As soon, however, as it enters the leaves, it becomes altered in a variety of ways, by the combined action of air, and light, and evaporation ; for which purposes the leaf is admirably adapted by its anatomical structure.

[blocks in formation]

Thus altered in the leaves, it ceases to be what we call sap, but becomes the proper juice ; or, in other words, acquires the peculiar character of the final secretions of the individual from which it is formed. Discharged by the leaves into the bark, it is thence conveyed by myriads of channels of cellular substance throughout the whole system. From these secretions, of whatever nature they may be, the fruit has the power of attracting such portions as are necessary for its maturation. Hence it follows, that the more we can increase the peculiar secretions of a plant, the higher will become the quality of its fruit ; and that, on the other hand, the less the plant is in condition to form those secretions, the less will be the quality of the fruit. It is for the purpose of producing the former effect that pruning and training trees are more especially destined. In pruning, we remove all those superfluous branches which overshadowed the remainder, and we endeavour to expose every part to the freest action of light and air. In training, the same thing takes place, but is increased ; there is not a branch that is not fully exposed to the most direct rays of light, and to the freest circulation of air, and even to the unimpeded action of the sun in aspects exposed to the south, east, or west. This action is obviously most powerful on the south, and hence the higher quality of fruits matured upon that exposure than on any other ; while, on the other hand, fruits raised upon a northern aspect are well known to be less highly flavoured than those from even an open standard.

For a similar reason, forced fruits, which are obtained at a period when there is little light, cannot be compared with those which are matured in the full blaze of a summer sun; and hence melons grown in frames covered with mats, and carefully excluded from the influence of that solar light which is indispensable to them, have, whatever may be their ex

atural

lan if

indi

pe of

at it INCated few iuch to prerds As al

of the

re,

a

ternal beauty, none of that luscious flavour which the melon, when well cultivated, possesses in so eminent a degree.

The next subject of consideration is the mode of multiplying improved varieties of fruit, so as to continue in the progeny exactly the same qualities as existed in the parent.

Unless we have the power of doing this readily, the advantages of procuring improved races would be very much circumscribed ; and the art of horticulture, in this respect, would be one of the greatest uncertainty. The usual mode of increasing plants, that mode which has been more especially provided by nature, is by seeds; but, while seeds increase the species without error, the peculiarities of varieties can rarely be perpetuated in the same manner. In order to secure the multiplication of a variety, with all its qualities unaltered, it is necessary that portions should be detached from the original individual, and converted into new individuals, each to undergo a similar dismemberment, with similar consequences. It happens that while in animals this is impracticable, except in the case of polypes, the system of life in a plant is, of all others, the best adapted to such a purpose.

We are accustomed to consider individual plants of exactly the same nature as individual animals: this is, however, a vulgar error, which is dissipated by the slightest enquiry into the nature of a plant. A plant is really an animated body, composed of infinite multitudes of systems of life; all, indeed, united in a whole, but each having an independent existence. When, therefore, any number of these systems of life is removed, those which remain, as well as those which are separated, will, under fitting circumstances, continue to perform their natural functions as well as if no union between them had ever existed. These systems of life are buds, each having a power of emitting descending fibres in the form of roots,

« ForrigeFortsett »