This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
[Translated from the "Journal de 1'Academie d'HorticuKare de Gand."]
Several persons having requested information as to the processes by which we may increase the size of fruits, we shall here point out the principal operations for obtaining this result.
Fruity like leaves, have the power of attracting the Bap from the root*, and of transforming it into cambium, or organizable matter. But ' contrary to that which takes place in the leaves, they employ all the cambium which they thus elaborate for their own nourishment. If the stock on which the tree is worked is naturally possessed of great vigor, the tree will produce numerous long shoots which will appropriate the greater portion of the sap, to the detriment of the fruits, which will consequently not attain a large size. They will, on the contrary, acquire a larger size if their absorptive power can counterbalance that of the shoots. It is for this reason that, all other things being equal, the fruit of trees worked on the quince stock is larger than that from trees worked on the pear stock. The same thing takes place with regard to apple-trees grafted on the Paradise, as compared with those on the Crab stock.
This operation, when well performed, has the effect of depriving the trees of a certain portion of their shoots. Hence it follows that a great portion of sap which would have been absorbed by the parts cut off goes to increase the size of the fruit. The object of summer pruning is likewise the complete or partial removal of a large number of shoots by disbudding and pinching. These operations also contribute to turn the sap to the benefit of the fruit; and under like circumstances, the fruit of well pruned trees is always larger than that from trees left unpruned.
If the mode of pruning adopted is such that the bearing shoots immediately proceed from the principal branches, the consequence is that the fruit receiving the sap more directly from the roots acquires a larger size. In fact, it is seen that fruit growing on the stem is always larger than that situated at the extremities of long Blender branches.
The quantity of sap, disposable for the growth of the tree, does not increase in proportion to the fruit which it bears. It is, therefore, apparent that the more numerous the fruits, the less the amount which each receives. Hence the utility of thinning, in order that those retained may be better nourished and become larger. The proper time for performing this operation is when the fruits are fully set.
If the length of the principal branches is to a certain extent diminished by shortening them at the winter pruning, a result analogous to that produced by ordinary pruning will follow; but the effect on the fruit is much more intense because the action of the sap is confined within narrower limits. It is. however, important to check in summer the vigorous shoots, of which a great number will be sure to make their appearance, otherwise they would absorb a large amount of sap to the detriment of the fruit.
The sap from the roots enters the fruit by means of vessels passing along the footstalk, and which ramify to an infinite extent throughout the cellular mass. Bulky fruits, such as pears and apples, soon attain such a weight that they exert a strain on their footstalks, which, by tightening the woody fibres and vessels, tends to collapse them. The tissues of the stalk being thus compressed, the passage of fluids is, to some extent, obstructed in that part Moreover, if fruits are attached to a branch having a more or less vertical direction, their gravity will cause a bending of the stalk, and will thus still further obstruct the passage of the sap. Again, it often happens that the fruit does not make an equal growth on both sides of its longitudinal axis, and a twisting of the stalk and strangling of the vessels take place, in consequence of which the circulation is partially intercepted. Now, if a support is placed beneath the fruit so as to prevent these effects on the stalk, it is very evideut that the sap will flow in much greater abundance into the fruit, which will then become larger.
This is the reason why those fruits which accidentally rest on branches or trellises are always of greater size than the rest.
In order that fruits may swell, their epidermis or skin must be continually expanding, so as to make room for fresh tissues which are forming in the interior, and the new fluids that are accumulating there. If all the parts of fruit are directly exposed to the full force of the sun and the drying action of the air, it will lose by evaporation an amount of fluid nearly equal to that which it receives from the roots, and its growth will therefore be less rapid. On the other hand, the tissues nearest the outside will acquire a greater degree of firmness, and lose to some extent their elasticity; they will offer more resistance to the expansion of the interior tissue, and will consequently restrict the growth of the fruit. If, on the contrary, the latter is kept in the shade, these influences will not affect it, and it will become larger. Indeed, this may be observed in the greater proportion of fruits covered by leaves as compared with those on the same tree, not so covered.;
It is necessary, however, in order that shading may not affect the quality of the fruit, to expose ' the latter when full grown to the direct action of the Bun. To diminished evaporation must also be attributed the considerable increase in size which always takes place in fruit introduced into bottles soon after it is set. The mouth of the bottle being closed after the portion of branch with the young fruit is introduced, the latter is secluded from the drying action of the air, and is constantly surrounded with a moist, warm atmosphere, which keeps the epidermis pliable, and stimulates the growth of the tissues.
We have already stated that fruit has the power of drawing towards it sap from the roots. If means can be found of stimulating its vital energy it will be perceived that it will absorb a greater amount of sap and attain a larger size. Now, M. E use be Gris has proved that a solution of sulphate of iron applied to the leaves has the effect of increasing their absorptive powers, and stimulating their cellular tissue; and it was only reasonable to suppose that salt would produce the same effect on the fruit • This, indeed, has been ascertained by M. Arthur Gris, who has continued the interesting researches of his father. He has proved that melons, and various species of fruit trees, the green parts of which had been watered on several occasions with a weak solution of sulphate of iron, yielded much larger fruits than those not so treated. One of my pupils repeated the same experiment in 1854 and 1855 on pear-trees. He gave the first watering as soon as the fruits were fairly set, in the end of June. He repeated the moistening every fortnight, in the evening, in order to prevent evaporation, and that absorption might be completely effected during the night. The solution was at the rate of 26 grains to a quart for the first three, and 35 grains per quart for the two last waterings.
He sent us, in the end of February from a tree thus treated, an Easter Beurre, so large that it could scarcely be recognized. He obtained like results in the following season.
But we doubt whether the results would not be still more successful if the fruits alone were moistened with the solution, for then they only would experience the stimulation of their absorptive powers, and would thus draw to themselves a much greater quantity of sap, inasmuch as the absorption by the leaves would be much less intense. Experiments should therefore be made with regard to this point.
Lancry exhibited to the Societe d'Agriculture de Paris in 1776 a branch of a plum-tree which ho had ringed. The fruits situated above the incision were much larger than those beneath it, and their ripening much farther advanced. Colonel Bouchotte, of Metz. thought of practicing this operation on vines, in order to accelerate their ripening. He ringed about 60 perches, and the grapes were larger and 15 days earlier. I have within the last twelve years repeated the experiment nearly every year on vines against walls, and always with like results. I have also tried it with the same success on the bearing shoots of the peach tree. It is necessary to perform the operation when the flowers are opening; the longer it is delayed after this period, the less is the effect produced. The incision should penetrate to the wood, and the ring of bark removed should have a width equal to half the diameter of the shoot. The width, however, should not exceed one-fifth of an inch, otherwise the wound will not close up, and the success of the operation will be affected.
For removing this ring of bark we have invented a small instrument, called a coupe-sive.
This proceeding is only applicable to apples and pears. [Chiefly to these we should say; for it has succeeded even in the case of stone-fruit]. A tree which in consequence of excessive vigor has never produced blossom buds, may by this means be made to produce fruit of large size from the abundant supply of sap which the inserted blossom buds will receive. But in order to derive the greatest benefit, it is necessary during the growing season to pinch the vigorous shoots of the tree, otherwise these shoots would absorb the largest portion of the sap to the injury of the fruit.
Professor Thouin describes Monographic des Greffes, a similar operation under the name of Greffe par approche Leberriays. M. Luizet, of Equilly, who certainly did not know of that description, again discovered this kind of inarching, and practiced it with the view of increasing the size of fruits. This is. how he operates: About the end of June he selects a vigorous shoot, which he inarches upon the peduncle of a fruit; then as soon as the union is effected and the shoot has grown sufficiently to draw the sap in large quantity towards the junction, he pinches the shoot in order to prevent it from absorbing too much sap to the injury of the fruit. When the stalk is too short, the shoot is inarched on the opposite side of the branch to that on which the fruit is situated. In both cases the shoot thus inarched acts as a nurse to the fruit, by drawing to its vicinity a large quantity of sap, Bud thus contributing to greatly increase its bulk. M Luizet exhibited, in September last, at the Exhibition of the Paris Horticultural Society, Easter Beurre and Grosse Calebasse pears, and likewise Clingstone peaches, which had been treated according to this method; and they were much above the ordinary size of these varieties.