This section is from the book "The Gardener's Monthly And Horticulturist V22", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
Prof. Karl Koch, in one of his lectures, says: "The view held by pomologists and fruit gardeners, that the nutritive substances move only in a downward direction, is refuted by their own practices.
" I would direct particular attention to the fact that all new growths and lengthening of the various axes of fruit trees (branches and twigs) takes place at the tips, and therefore it is at these points that the greatest quantity of nutritive substance is required, and consequently the greatest flow is not downwards but upwards. Moreover, when the cultivator wishes to cause a latent bud to push forth, which in its action is a consumer of food, he should, acting under the same view, make his incision below the bud in order to divert the greatest quantity of nutritive substances to the new growth; but he does not make it below the bud, he makes it above. As a matter of fact the nourishment which should go to the upper part of the axis is impeded in its upward course by the incision, and actually serves to develop the dormant bud. Again, why does the gardener pinch back the tips of shoots in spring? It is either to strengthen a fruit-bud below, or indeed to bring it to development. The nourishment that would have been used in the elongation of the shoot now remains to benefit the fruit-buds below".
We do not think intelligent pomologists in this country believe that nutritive substances do not flow upwards. After all, it is a question what the Professor meant by " flow of nutritive substance." New growth is formed by the continuous germination of cells. In the primal cell of the season nutrition is stored from the accumulations of last year, and the successive new growths are formed from these stores for some time after the growing season opens. To this extent nutrition may be said to have an upward flow. But that there is also a downward flow, every gardener knows who has had any experience in layering. A stool plant may in time be utterly destroyed by persistent layering of all its branches; the "downward" flow of nutrition reaching only to the roots of the layered branch, and literally starving the old plant though with numerous roots of its own - and it is from the knowledge of this fact that layered plants of grapes are not valued, because a stool kept for layering comes in time to have a low vital power, laying the progeny open as an easy prey to diseases.