The natural history of plants, their forms, growth, reproduction, and distribution; . wisting of the petioles goes hand in hand with that of the inter- 418 RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. nodes. The torsion of the leaf-stalks of the Judas Tree (Cercis Siliquastrum),where this alone occurs, without a simultaneous twisting of the internodes, isparticularly striking. The leaves of the plant, as can be seen on the erect twigs,and especially well in the suckers, are arranged in the one-half phyllotaxis, two rows. The leaf-blades on the erect branches are parallel wit
The natural history of plants, their forms, growth, reproduction, and distribution; . wisting of the petioles goes hand in hand with that of the inter- 418 RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. nodes. The torsion of the leaf-stalks of the Judas Tree (Cercis Siliquastrum),where this alone occurs, without a simultaneous twisting of the internodes, isparticularly striking. The leaves of the plant, as can be seen on the erect twigs,and especially well in the suckers, are arranged in the one-half phyllotaxis, two rows. The leaf-blades on the erect branches are parallel with the a sucker be cut off and held horizontally, all the leaf-laminae will be directedat right angles to the earth. One might perhaps expect that they would alsoassume this direction if the twig had grown horizontally. Anything but that,however. The stalks of all the leaves twist round instead, until the laminae,or blades they bear, are again placed in a direction parallel with the ground onthe horizontal branches, and the result is that the leaves on all the branches of. Fig. 108.—Horizontally growing leafy twig of the Paper Mulberry-tree (Broussonetia papyri/era). the Judas Tree, whether erect, oblique, horizontal, or inclined towards the earth,always present the same attitude to the incident light. The third case, the alteration in the inclination of the blade to the leaf-stalk,which, on the whole, is but seldom met with, is represented in the best knownexample, the cursorily mentioned Japanese Paper Mulberry (Broussonetia pa2Jy-rifera) in fig. 108. In this plant the leaves are decussate, arranged in fourrows, each pair of leaves being inserted at the same level, and the successivepairs alternating at right angles. In erect twigs, therefore, they display thearrangement seen in the twigs of maple (see fig. 106) or of Diervilla (seefig. 107 ^). The following alteration, however, is seen to occur in the horizontalbranches of the lower boughs of the Paper Mulber
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1902
