Page:Popular Science Monthly Volume 27.djvu/364

348 In the beech, the general plane of the leaves is again that of the branch (Fig. 2), but the leaves themselves are ovate in form, and smaller, being only from two to three inches in length. On the other hand, the distance between the internodes is also smaller, being, say, one and a quarter inch against something less than two inches. The diminution in length of the internode is not, indeed, exactly in proportion to that of the leaf, but, on the other hand, the leaf does not make so wide an angle with the stem. To this position is probably due the difference of form. The outline of the basal half of the leaf fits neatly to the branch, that of the upper half follows the edge of the leaf beyond, and the form of the inner edge being thus determined decides the outer one also.

In the nut (Corylus), the internodes are longer and the leaves correspondingly broader. In the elm (Ulmus, Fig. 3), the ordinary branches have leaves resembling, though rather larger than, those of the beech; but in vigorous shoots the internodes become longer and the leaves correspondingly broader and larger, so that they come nearly to resemble those of the nut.

But it may be said the Spanish chestnut (Castanea vulgaris, Fig. 4) also has alternate leaves in a plane parallel to that of the branch, and



with internodes of very nearly the same length as the beech. That is true; but, on the other hand, the terminal branches of the Spanish chestnut are stouter in proportion. Thus, immediately below the sixth leaf, the chestnut-stalk may be ·15 of an inch in thickness, that of the beech not much more than half as much. Consequently, the chestnut could, of course supposing the strength of the wood to be equal, bear a greater weight of leaf; but, the width of the leaf being determined by the distance between the internodes, the leaf is, so to