This section is from the book "The Gardener V2", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
This phrase has a rather learned and respectable sound when used by a writer on the subject of roots or branches, and is supposed to express much or little meaning just according to circumstances; but it is a much-prostituted term, and ought to be properly cleared up. The words were, we believe, invented by the physiologist to denote some kind of sympathetic action existing between the roots and the top of a tree - akin to that which is said to exist between the dog's head and its tail; but what that sympathy is, and where it begins or ends, nobody knows, although its presumed existence is made to do duty in a hypothetical capacity on many occasions. Teetotallers say the tippler's general apology is, that he requires spirits in winter to keep him warm, and in summer to keep him cool; and gardeners and botanists, it is to be feared, employ "reciprocal action" on the same principle - it is a good peg. We are taught that if we want to create superabundant vigour in a vine or other tree, we must encourage growth in order to encourage roots, and a corresponding development of both; and next, that the way to increase the vigour of the same tree is to cut all this growth away at the winter pruning, or nearly all, - two quite opposite methods of attaining the same end.
One much-respected and noted author is at great pains to explain, physiologically, how the top limbs of certain horizontally-trained fruit-trees are very apt to grow over-luxuriantly at the expense of the lower ones unless persistently checked by the stopping of the summer's growth; and in the same breath it is also stated that in order to make the weak lower branches stronger, they must be pruned back severely : and it is all connected in some mysterious way with "reciprocal action" - so we are told. It has struck the writer frequently that it must be a marvellously consistent theory which teaches that in order to produce vigorous Vines, for example, we must encourage them to produce as many limbs and leaves as possible the first year or two, and then cut all the said limbs off at pruning-time for exactly the same reason that they were encouraged to grow. A greater writer than practitioner has written and explained how the leaves pump up moisture with astonishing force, and that the more pumps the more roots - i.e., reciprocal action - forgetting that some plants, like the Vine, send up their sap with the greatest mechanical force when there are no leaves, otherwise pumps, upon the tree at all.
But though the cultivator blames the branches for encouraging the roots - or, as was said lately, " it is the leaves that apply the stimulus to the roots " - he does not act as if he believed it; for when his trees grow over-strongly, he makes no pretence of controlling the roots by cutting off the branches, but sets about controlling the branches by cutting off the roots. In practice he finds himself totally unable to make his theories fit. We have, indeed, neither the head nor the tail of a theory in many things we do in the garden. In dealing with such questions there is a tendency to forget what Dr Lindley used to say underlay all other problems of vegetable physiology, and that is vital force - life. So far as the practical application of the theory of reciprocal action is concerned, the despised Chinese gardeners are far more consistent than we are. The Chinese theory is, that it is the roots which apply the stimulus to the branches; and they adapt their practice accordingly, and succeed admirably. They scout the idea of restraining root-action, or top vigour either, by curtailing the branches; but they do restrain the roots, and by that means alone they make the smallest dwarfs of the greatest giants of the forest.
Their Oaks in thumb-pots and Mandarine Orange-trees are never pinched nor pruned, and yet they are always veritable dwarfs. The Chinaman, in short, sets out with the assumption that the vitality lies in the roots, and he troubles himself about neither stocks nor pruning, and beats us hollow in the production of dwarf-trees and fertility in whatever subject he tries his hand upon. This may not be reckoned a "practical article" by some of your readers, but it suggests practical ideas, and the subject is one that has been present to my mind on many occasions in connection with work, and it is not unworthy of further consideration, as it raises questions that go to the root of many cultural operations. J. S., W.