The natural history of plants, their forms, growth, reproduction, and distribution; . rises vertically from the horizontaltwig; the leaf-blade it supports is bent down at right angles from it, and conse-quently is here again parallel to the surface of the ground. A slight torsion ofthe internodes, a shortening of the erect leaf-stalks, and a diminution of the leaves RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. 419 borne by them, certainly assist in the completion of this peculiar arrangement ofthe leaves; the above illustration will demonstrate other particulars far better thanthe most
The natural history of plants, their forms, growth, reproduction, and distribution; . rises vertically from the horizontaltwig; the leaf-blade it supports is bent down at right angles from it, and conse-quently is here again parallel to the surface of the ground. A slight torsion ofthe internodes, a shortening of the erect leaf-stalks, and a diminution of the leaves RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. 419 borne by them, certainly assist in the completion of this peculiar arrangement ofthe leaves; the above illustration will demonstrate other particulars far better thanthe most detailed description. The elevation of individual leaf-stalks above the horizontal branches occurs,somewhat more often in low semi-shrubs and herbs, than in trees and shrubs,whose shoots, furnished with decussate leaves, come to lie flat on the ground,as in some species of speedwell (Veronica officinalis and Chamcedrys), and inmany species of Rock Rose (Helianthemum). In the large-flowered Rock Rose(Helianthemum grandifiorum), an erect branch of which is illustrated in fig. 107 ^. Fig. 109.—Leafy Twig projecting laterally from the Stem of tne Norway Maple (_Acer platanoides). the leaves are arranged in pairs and placed crosswise, so that they occur on thestem in four rows. If such a shoot bends down over the ground, a slight twistingof the leaf-stalks occurs first of all, so that their leaf-blades come to lie parallel tothe soil; but another alteration is yet to be noticed. In every alternate pair ofleaves one of the leaf-stalks rises up, and its blade is bent down almost at a rightangle and lies above the horizontal stem as shown in fig. 107 \ In consequence ofthis alteration of position the leaves no longer form four rows as on the erectshoots, nor two as in Diervilla, but three rows, the middle one, however, consistingof a smaller number than the two side rows. The fourth case, which still remains to be discussed, is the increase in length ofindividual leaf-stalks. It may
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1902
