This section is from the book "The Gardener's Monthly And Horticulturist V25", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
A few months ago we were called on to notice Dr. Hough's Elements of Forestry, and we stated that cuts made to illustrate one point, did not always represent the whole case accurately. Reference was made to a cut of two year old wood of English oak "borrowed from Rossmasster's work." which showed only four "hairlines" in one annual circle of wood, when there should be a very much larger number; and that the dots should be on the inner instead of the outer circle of the commencing season's growth. In regard to this latter statement two correspondents have written to us, one kindly suggesting that the remark was "inadvertently" made. But it was deliberately written, and was in the writer's mind chiefly from personal examination mule during the Centennial year, in comparison with Japan and other woods. That there must have been some mistake the writer now believes from the fact that though very much difference exists in the appearances, the little holes or dots seem always larger in the courses which commence the season's growth than in those which follow, sometimes almost wholly disappearing before the season's growth ends. In other respects, however, the criticism seems just, and we give the following illustration which we have had made for this note.
It is from the leading shoot, two years old, of a ten year old English oak, grown at German-town, and enlarged to a little over double its natural size.
This cut represents with tolerable accuracy a. cross-section of a two-year-old piece of wood. The star-shaped outline of the pith is well represented, then we have eighteen "hair-lines" to the apex of the convex bend, and twenty-four to the concave portion of the line. Small dots of uniform size are scattered freely over the whole surface, though in more or less perfect radial lines. When the next season's growth commences the ducts are larger, and seem to be arranged in a more or less broken circle. In endeavoring to show this larger sized duct, the artist has placed the "hairlines" together closer than they are in the copy given him, and this makes the commencement of the annual growth appear of a darker shade than the other portion of the wood. There is really no difference in the color of the wood, or in the width apart of the "hair lines," and there is nothing whatever to show where the growth of one year ends and the other begins except the more circular arrangement of the dotted ducts, their greater number, and slightly larger size. Those who are fond of looking into nature for themselves will find a study of wood with a good pocket lens very fascinating.
No two species will be found the same in respect to the arrangement of these ducts, nor what for popular comprehension's sake we have called the " hair lines " as seen in this cut. In some cases the dots are of equal size, spread almost equally over the surface, and giving not the faintest clue as to where the growth of one season ends, or another begins. Sometimes we may be able to tell with considerable certainty the age of a tree from its "annual rings," but many trees will not give it accurately, and we are not sure but those which seem to give us the data with considerable regularity, often vary from their plan.
In the cut will be noted some features which we do not remember to have ever been referred to by those elementary works which treat of the formation of wood. It will be noted that the outline given by the bark is formed of segments of five circles, and that the bark is of double the thickness and forms a parallelogram where these segments meet. These rectangular blocks of bark are opposite the bays in the star formed by the pith in the center. The center of the arm of the star corresponds to the center of the arc in the outline of the wood. From each sinus in the star to the rectangular blocks of bark, are two nearly parallel lines. The whole piece of wood is thus divided into five sub-triangular segments. The little "hair lines" crossing the two parallel ones, do not connect with the lines enclosed by the triangle, but they are uniform in number with them.
It would be foreign to our present purpose to go into any explanation of the morphological interpretation of the pentamerous plan on which the trunk of an oak tree is seen to be formed. All we have room for is to give a brief explanation of what the "hair lines" mean. There has been a great deal of unnecessary mystery thrown around the formation of wood. We are told about the annual concentric "layer" of wood, and the cambium "layer," and other "layers," as if a new plaster of material was placed over the old wood, which in time became a solid layer stuck over the old one. The idea is much as we might gather from the making of a candle. The wick is first dipped into the molten fat, then drawn out to cool - then dipped in and out again, every time getting larger by the accretion of the cooling liquid. But wood is not made in this way. There is no evidence that anything which has life came directly from inorganic elements. That which is alive came from that which had life before it. All things spring from an egg, and the cells out of which the trunk of a tree is formed are no exception. Every living cell sprung from a parent cell, and the cells out of which this season's wood is formed, came in a direct line from the cells of the year before.
The mass of mucilage between the bark and the wood, called by Grew "Cambium," and which is supposed to generate the cells which are to form a new "layer" of bark and wood, does nothing of the kind. It furnishes simply food for the new cells which push out from the mother cells just behind them. Now the "hair lines" in the cut show the successive generations of these cells during the growing season. In our piece of two year old wood, there are twenty-four concentric circles in the year instead of merely "one annual layer," in the sense in which this expression is usually understood.
We have purposely avoided in this little sketch, using the language of science to describe this process of forming the annual growth of wood. The object is to convey to those who are unacquainted with this language, some idea of what they may know more about if they care to pursue the study further as a matter of science.