The natural history of plants, their forms, growth, reproduction, and distribution; . onger extended horizontally, but rather in an upward direction, and form anangle with the stem which is less than a right angle; and the highest leaves evenapproach the upright, their midribs lying in the plane of the incident noondayrays. In accordance with this adjustment, an alteration of the dimensions, particularlyof the length of its leaves, may be observed at different heights of an erect thickly- 410 RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. leaved stem. The lowest leaves originating next th
The natural history of plants, their forms, growth, reproduction, and distribution; . onger extended horizontally, but rather in an upward direction, and form anangle with the stem which is less than a right angle; and the highest leaves evenapproach the upright, their midribs lying in the plane of the incident noondayrays. In accordance with this adjustment, an alteration of the dimensions, particularlyof the length of its leaves, may be observed at different heights of an erect thickly- 410 RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. leaved stem. The lowest leaves originating next the soil are the longest; the leavesnext above these are, on the other hand, visibly shorter, and often in the region ofthe flowers are changed into insignificant scales closely applied to the stem. It caneasily be seen in every plant of the Shepherds Purse (Capsella Bursa pastoris), onevery mullein (Verbascum), and every hawkweed (Hieraciuvi), that such smallupwardly-directed leaves cannot injure by overshadowing the leaves growing belowthem either in the same or in adjacent row^ Fig. 103.—leaf-mosaic Leaf-rosettes of a Cranes-bill {Geranium Pyrenaieum) seen from above. 2 Leaf-rosettes of a Saxifrage (Saxi/raga Aizoon).s Leaf-rosette of a Bell-flower (Campanula pusilla) seen from above. ?» Adpressed scale-like leaves on the twig of anArbor Vitae (Thrtja). Many plants produce within a year, at the ends of their upright shoots, a largenumber of leaves which radiate out from the stem with very small horizontaldivergencies, standing close above one another, and forming a so-called rosette. Inorder that all the leaves of such a rosette may receive an equal proportion of light,it is absolutely necessary that the upper leaves should be considerably shorter thanthe lower. And in all rosettes this is actually the case. However, some veryinteresting modifications are to be seen. In rosette-forming succulent plants (,Echeveria and Sempervivum), and in many saxifrages (Saxifraga),
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1902
