File:The natural history of plants, their forms, growth, reproduction, and distribution; (1902) (14783539625).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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are borne on very long stalks. The disc-shaped leaf-blades lie with their under side on the surface of the water, while their upper surface is exposed to the air. The leaf-stalks thus traverse- the whole depth of the water, and look like ropes by which the floating leaf-discs are anchored in the muddy bottom. The long scapes,terminating in floating flowers, serve a similar purpose. Here also must be included the aquatic fern-like plant - Marsilea. Its leaves remind one of those of the Wood Sorrel. The Frog-bit (Hydrocharis) and the Villarsia (Limnanthemum) form a fourth group, not unlike water-lilies on a small scale. Their leaves and flowers, however, do not arise directly from the main stem (as in the last group), but from long lateral shoots, quite bare of leaves, till just close to the surface (cf. vol. II., fig. 419). Our fifth group includes forms transitional between the groups already described and the sixth and largest group. They include forms with
[plate page title :] PROCUMBENT AND FLOATING STEMS. 667

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Fig. 155 — Vallisneria spiralis
[next page title :] 668 PROCUMBENT AND FLOATING STEMS.
finely-divided, submerged leaves, in addition to orbicular floating ones as in the water-lilies, &c. Such plants are known as heterophyllous (plantae heterophyllae). Examples are furnished by several potamogetons (Potamogeton heterophyllus, rufescens, spathulatus), some water-crowfoots (Ranunculus aquatilis, Baudotii, hololeucus), the Cabomba (Cabomba aquatica) and the Water-chestnut (Trapa). In the sixth group the plants are firmly rooted in the mud like those of the former group, but the shoots rising from them bear only submerged, thin and limp leaves. These plants in descriptive botany are called submerged (plantae submersae). Their leaves — arising from the much-branched filamentous stems — exhibit an endless variety of form. They are sometimes decussate, sometimes spirally arranged, often broad and embracing the stem, and then again fall into the opposite extreme, and form long very narrow ribbons or threads. Frequently they are reduced to mere bristles.

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