Elementary Notes on Conifers (Classic Reprint)
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| Hersteller: | Forgotten Books (Church, A. H.) |
| Stand: | 2015-08-04 03:50:33 |
Produktbeschreibung
Excerpt from Elementary Notes on Conifers Land Flora: as constituting the autotrophic vegetation of subaerial environment (beyond the horizon of saprophytic phyla of Fungi), expresses the progression of plant-life from the medium of water to that of atmosphere; involving not only the factor of diminishing water-supply (ultimately reduced to a vanishing point), but more definitely that of nutrition in terms of food-salts no longer available in the general medium, and implying the mechanism of absorption, conduction, and transpiration. Older phases of sexual reproduction, involving fertilization by mobile gametes in a watery medium, are long retained; but dispersal is provided for by the evolution of wind-borne spores, in a manner paralleling that of many subaerial Fungi, as spores produced in a sporangium. Three main lines of advance, roughly indicated as (i) Bryophyta (Mosses),(2) Pteridophyta (Ferns),(3) Phanerogams (Seed Plants), not necessarily in linear sequence, are to be regarded as parallel phases of progression, passing successively to higher stages of land-organization. Bryophyta, including Mosses (Bryineae), with Liverworts (Hepaticae) and Jungermanniae: one general plan of organization and life-cycle common to all, and the plant-types of no great size or importance: Sphagnum, the Bog-Moss, alone attains special economic and geographical significance. The Life-cycle presents a definite alternation of generations, in which the sexual phase is still dominant, as the individual receiving the name, and is attached to the substratum by rhizoids, absorbing freely over its entire surface; hence requiring a saturated atmosphere, or copious atmospheric precipitations. The sexual organs are antheridia (o)and archegonia(5); the flagellated antherozoids are 2-ciliated; the oosphere is solitary in the venter of the archegonium, and is fertilized in sihi. The zygote (oospore) develops directly to a parasitic sporophytic phase, which remains permanently attached to the gametophyte, being wholly dependent on it for water-supply, and reducing to a simple capsule-like body sporogoniuvi), more or less stalked, and devoted to the production of air-borne spores: the latter are produced in great numbers, in tetrad-groups following a stage of meiosis. All the types are more or less decadent, and may be regarded as vestigial relics, restricted to distinctly inferior biological stations; e.g. mosses on walls or in shady hedges, on peaty soil, among grass, on the bark of trees, especially in tropical rainforests: from the standpoint of higher vegetation an indication of inferior or ill-drained soil. The more familiar and more striking types include: - I. Polytrichum commune, a large tussock-form, the shoots of the gametophyte growing in close association, a foot high or more, and bearing short acute leaves in spiral sequence. The apex is controlled by a 3-sided apical cell, each segment from which produces a leaf: the leaf-laminae bear plates of protosynthetic tissue on their upper surface, and the growing-point is enclosed in a bud-aggregate. Archegonia and antheridia are produced in spring at the apices of special shoots, the latter in lateral groups in leaf-axils. Fertilization effected in rain-water (May); the embryo grows in the enlarged archegonial cavity, taking up a portion of it with shaggy hair-growth as calyptra, and elongating to a stalk seta2-3 in. long, and a radially symmetrical capsule(7 mm.): the latter differentiates a wall, air-spaces, archesporium, columella, c.; an apopkyst s-region with stomata, intercellular spaces, cuticle, implies a transpiration-mechanism. The archesporium gives rise to sporetetrads, and finally spores, 10 diam.; the apex differentiates a conical operculum which is shed to expose the peristome-xtgxoxv of teeth and epiphragm, constituting a sprinkling-
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