The natural history of plants, their forms, growth, reproduction, and distribution; . ndhorse-chestnut treesfurnish strikingexamples of phenomenon isshown still betterin firs (see fig. 105),in which the twigsspringing from thelowest branches fre-quently rise almostvertically. This last circumstance is also of interest in so far as it indicatesthat it is not only the weight of the leaves which brings about the altereddirection of the branching, but that it depends also on other conditions, to bediscussed later on. In the terminal twigs of the lowest branches, which are again turned upw
The natural history of plants, their forms, growth, reproduction, and distribution; . ndhorse-chestnut treesfurnish strikingexamples of phenomenon isshown still betterin firs (see fig. 105),in which the twigsspringing from thelowest branches fre-quently rise almostvertically. This last circumstance is also of interest in so far as it indicatesthat it is not only the weight of the leaves which brings about the altereddirection of the branching, but that it depends also on other conditions, to bediscussed later on. In the terminal twigs of the lowest branches, which are again turned upwards,the same distribution and direction of the leaf-blades as are displayed by theerect twigs of the summit will naturally be resumed; but it is not so in the caseof those twigs which retain a horizontal direction, or whose summits are eveninclined towards the ground. Suppose that the maple-twig, which is illustratedhere, has not grown from a central bud of the summit, and does not rise verticallyupwards, but that it has been developed from an older, lower branch, and is extended. Fig. 106.—Erect leafy Twig of the Norway Maple (Acer platanoides) RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. 417 almost horizontally. If the surface of the foliage-leaves on the horizontal twigretains the same direction as those on the erect twig here represented, this willbe the most disadvantageous position imaginable with regard to the incident is urgently necessary that they should alter this position and again arrangethemselves suitably. This rearrangement of the leaf-surfaces proceeding fromthe horizontal twigs is carried out, and, indeed, in four different ways. Eitheran adequate twisting of the internodes is effected; or a twisting of the leaf-stalksoccurs; or the leaf-stalks do not undergo actual torsion, but their inclinationto the leaf-blade becomes altered; or, finally, individual leaf-stalks lengthen to anextraordinary extent; so that the blades borne by them are carr
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1902
