A correspondent sends us the following editorial from the London Garden, with the note that it might be of some interest to republish it for the benefit of American readers. It so happens that it has appeared - years ago - in the Gardeners' Monthly. It was written by the Editor of the Gardeners' Monthly - and its appearance as an "editorial" somewhere else ought not to give it any additional value. To oblige our correspondent we however republish it:

"In many trees the annual layers are so regular, and seem to be placed so nicely, that one not a botanist might be pardoned for believing that the sap was changed to wood matter in the leaves, and the new-formed matter sent down, sliding over the old layer like the section of a telescope; but, though the food was prepared by the leaves in a great measure, the actual growth was made by the germination of some of the cells along the whole outside wall of last year's wood beneath the inner bark. The germination of the cells takes place about the middle of June. Take a healthy cherry tree and strip it entirely of its bark to any length desired. At that season a viscid liquid will be found covering the woody surface in abundance. The stripped part is covered with a cloth to prevent evaporation, and in a few days numerous dots, like needle points, will be seen about the sixteenth of an inch apart all over the surface. These are the young cells which have germinated from those of last year. They continue germinating, one from the other, until they meet, when they unite and form a complete surface.

In the autumn a layer of wood will be found just as thick as in the part of the tree not dibbarked, and a single layer of liber, with its outer coat of cellular matter - perfect bark - will have been formed over the whole. The entire formation of wood and bark can thus be seen by the ordinary observer without the necessity of any nice microscopical work. Other people have tried the experiment with other trees. We have seen large apple trees that have had their bark peeled wholly off from their trunks, at the season named, make an entire new layer of bark and wood, not only with no injury to the tree but to its manifest enjoyment; but our own experiments were confined exclusively to the cherry. By this experiment we learn that there is no difference primarily in any part of the annual covering. The same cell may become permanent tissue, or generating tissue, and from the generative tissue may come, before the season of growth closes, every form of structure known to anatomists, from pure wood to the outermost cuticle of the bark. How these cells become differentiated may be passed over here. We know that cell growth is not always uniform in its operations.

The law that changes the outermost series of newly made cells into liber need not necessarily operate so exactly as to make them perfect to this end - a few may be thrown off into the liber as generative tissue - and, granting this possibility, we see how the woody granules in the apple are formed".