File:The natural history of plants, their forms, growth, reproduction, and distribution; (1902) (14803344723).jpg

Identifier: naturalhistoryof01kern (find matches)
Title: The natural history of plants, their forms, growth, reproduction, and distribution;
Year: 1902 (1900s)
Authors: Kerner von Marilaun, Anton, 1831-1898 Oliver, Francis Wall, 1864- Macdonald, Mary Frances Ewart Busk, Marian Balfour, Lady
Subjects: Botany
Publisher: London, Blackie
Contributing Library: NCSU Libraries
Digitizing Sponsor: NCSU Libraries

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ee fig. Ill ^), that larger and smaller leaves are here arrangedin quite a peculiar manner. The larger leaves stand in two rows, and in virtueof their shape it happens that, between every two, gaps are left near the stem. 422 RELATION BETWEEN POSITION AND FORM OF GREEN LEAVES. These cannot be of use as apertures, through which light can pass to leavessituated below, for the simple reason that, as a rule, no other leaves requiring lightare to be found under the branches in question. Smaller green leaves are nowinserted in these gaps, which serve as protective leaves for the flowers, that is,indirectly for the fruits, but whose function also coincides entirely with that ofthe large foliage-leaves. The small leaves twist and turn until each comes to lieexactly in the middle of a gap, where they neither encroach upon the large leaves,nor are encroached upon by them. An exactly similar insertion of smaller leavesin the gaps between the larger can also be observed in the Thorn-apple (Datura
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Fig. 112.—Mosaic of Unsymmetrical Leaves of unequal size.Leafy horizontal Twig of an Elm (Ulmus) seen from above. Stramonium), and in Imjjatiens parvijlora, illustrated respectively in fig. 104 ^and fig. 104 \ This mosaic-like fitting together of larger and smaller bladesappears to be combined with the want of symmetry of the leaf-base in short-stalked leaves, as e.g. in the wall-climbing stem of Ficus scandens (see fig. 110 2),and on the older horizontal branches of elms (Ulmus), one of which is illustratedin fig. 112. It has been already mentioned that the blades with erect petioles,arranged in the central rows on the Paper Mulberry, are considerably smaller thanthe lateral rows of leaves with horizontal stalks (see fig. 108). This difference inthe size of the central and lateral rows of leaves on horizontal stems is verynoticeable also in the dainty selaginellas, belonging to the family of Lycopodiaceae,of which a species (Selaginella Helvetica) is represented in fig. Ill \ It is

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