. Un manuel de botanique pour les collèges et universités ... La botanique. 6o6 mince, feuilles de la rosette de l'écologie sont plus divisés que sont le petit 1 hick, feuilles de la tige. Cytisus scoparius dans les trois lobes lovi^er feuilles sont suivies par de simples (ou plus correctement, l'un à lobes) feuilles, fortement réduite en taille, et dans le japon ivy les feuilles inférieures sont trois-parted, tandis que les feuilles supérieures sont simples (bien qu'avec une nervation palmée semblable) et souvent aussi grand que ou même plus importants que ceux ci-dessous (fig. 887, 888). Dans les souches intermédiaires Leonurus cardiaca feuilles sont plus divisés que sont celles ci-dessous ou. Fig. 889-89

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. A textbook of botany for colleges and universities ... Botany. 6o6 ECOLOGY thin, rosette leaves are more divided than are the small, 1 hick, stem leaves. In Cytisus scoparius the three-lobed lovi^er leaves are followed by simple (or more correctly, one-lobed) leaves, greatly reduced in size, and in the Japan ivy the lower leaves are three-parted, while the upper leaves are simple (though with similar palmate venation) and often as large as or even larger than those below (figs. 887, 888). In Leonurus Cardiaca the intermediate stem leaves are more divided than are those below or. Figs. 889-894. — Leaf variation in the motherwort {Leonurus Cardiaca); 889, a basal rosette leaf; 890, one of the more apical rosette leaves; 891, a leaf from the lower part of a stem; 892, 893, leaves from the upper part of a stem; 894, a leaf from the floral region; note that lobation and leaf size increase for a time, culminating in 891, and reach- ing a minimum in 894. above (figs. 889-894), and in Sassafras almost any leaf may be entire or variously lobed, apparently without relation to transpiration or nutrition, or even to the phenomena of rejuvenescence. One of the most extraor- dinary cases of leaf dimorphism is exhibited by the staghorn fern (Platycerium), in which there are erect leaves that bear the sporangia, and sterile leaves that adhere closely to the ground and keep the substra- tum constantly moist. The sterile leaves appear to react to contact and gravity rather than to light, ultimately forming an overlapping series, the lowermost of which gradually become transformed into humus. The advantages of leaf variation in land plants. — In so far as the basal or lower stem leaves of any plant are large and thin, they favor. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Coulter, John Merle, 1851-1928;

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