The natural history of plants, their forms, growth, reproduction, and distribution; . 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 proceedin
The natural history of plants, their forms, growth, reproduction, and distribution; . 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 carried far beyond. Fig. 107.—Twisting of Internodes and Leaf-stalks. Erect twig of tlie large-flowered Rock Rose (Helianthemum grandiflorum). * Procumbent twig of the same Erect twig of Diervilla Canadensis. * Twig of the same plant, bent downwards. their neighbours. It naturally very frequently happens that these alterationsare also combined in many ways. The first instance, the twisting of the internodes, may be observed in hazelsbeeches, and hornbeams, and especially in trees, shrubs, lianes, and bushes withdecussating short-stalked leaves, as for example in Gornus and Thunhergia, inLonicera and Diervilla, in Androscemum and Hypericum, in Thymus and Vinca,Coriaria myrtifolia, Gentiana asclepiadea, and innumerable others. Fig. 107 ^represents an erect twig of Diervilla Ganadensis. As soon as such a twigdevelops no longer upwards, but horizontally, a twisting of 90° takes place in eachinternode, and the consequence is that the surfaces of all the pairs of leaves takeup the same
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1902
