The natural history of plants, their forms, growth, reproduction, and distribution; . ORM OF GREEN LEAVES. 423 plane, is observed especially in plants growing in dark or half-shaded they do not require to protect themselves against an over-abundance of light,but on the contrary have to make what use they can of its scanty amount, andthis is best effected by the fitting together of all the leaves on a stem in one plane,like the stones of a mosaic. It is, of course, not so easy to produce a mosaic fromsymmetrically circular or elliptical leaves; but unsymmetrical, or rhomboidal,tria
The natural history of plants, their forms, growth, reproduction, and distribution; . ORM OF GREEN LEAVES. 423 plane, is observed especially in plants growing in dark or half-shaded they do not require to protect themselves against an over-abundance of light,but on the contrary have to make what use they can of its scanty amount, andthis is best effected by the fitting together of all the leaves on a stem in one plane,like the stones of a mosaic. It is, of course, not so easy to produce a mosaic fromsymmetrically circular or elliptical leaves; but unsymmetrical, or rhomboidal,triangular, pentagonal, and, generally, polygonal blades lend themselves particularlywell to this arrangement. Excellent examples of this are furnished in the leaf-mosaics in fig. 110, as well as in the elm twig represented opposite. The leaf-mosaicformed by the ivy on the ground of shady woods is particularly instructive inthis respect. In the picture below, which is a faithful reproduction of a pieceof ivy carpeting the ground of a wood, it is seen how the lobed, five-pointed leaves. Fig. 113— on the ground of a forest. have in the course of time fitted into one another. The lobes and points of one fitinto the indentations of another, and thus originates a layer of leaves than whichone better fitted to the given external conditions could hardly be imagined. In thismosaic, indeed, we no longer see two rows of leaves symmetrically arranged on thehorizontal stem. What manifold elevations and depressions, torsions, displace-ments, and elongations must have taken place in order to produce such a leaf-mosaic from the regular rows of leaves! But we learn from the consideration of allthese instances, that not only the arrangement and distribution of the foliage, andthe direction and length of the leaf-stalks, but the size and even the shape ofthe leaf-blades also, and the resultant mosaic-like piecing together, stand in causalrelation to the conditions of illumination; a
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1902
