File:Text-book of structural and physiological botany (1877) (14753689636).jpg

Identifier: textbookofstruct00thom (find matches)
Title: Text-book of structural and physiological botany
Year: 1877 (1870s)
Authors: Thomé, Otto Wilhelm, 1840- Bennett, Alfred William, 1833-1902
Subjects: Plant physiology
Publisher: New York : J. Wiley & sons
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library

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ced each from a singleepidermal cell, and therefore of the nature of trichomes, asin Ferns ; but are rather entire lobes of the leaf, the internaltissue of which is the origin of the mother-cells of thespores. In Ophioglossum the sporangia are arranged in tworows in a simple spike (Fig. 446 i., 11.), and are coherent;in Botrychium^ on the contrary, they are distinct, and forma branched spike or panicle. The tetrahedral spores pro-duce, on germination, prothallia, on which are developedthe reproductive organs, antheridia and archegonia ; butthe process of impregnation and the first stages of develop-ment of the oospore have not yet been observed. There isthe same alternation between a sexual generation producingantheridia and archegonia, and a non-sexual generation pro-ducing spores, as in the last two classes. In Ophioglossum special Morphology and Classification, 323 there is also a vegetative mode of reproduction by means ofadventitious buds on the roots (Fig. 446 i.). The prevalent
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Fig. 446.—Adders-tongue, Ophioglossum vulgatmn ; I. whole plant (natural size) •U. a part of the fertile portion of the leaf with four sporangia in the act of burst-ing (magnified). Y2 324 Structural and Physiological Botany, form of tissue is parenchymatous fundamental tissue, con-sisting of long, nearly cylindrical cells, thin-walled and fullof sap, and with large intercellular spaces. Both sides of theleaves are covered by an epidermis provided with numerousstomata. The vascular bundles form a network in the stem,the tissue which occupies the space between the meshesbeing frequently changed into scalariform vessels, so thatthe stem then forms a closed hollow cyUnder. This oftentakes place only on one side. (The adders-tongue, Ophioglossum vulgatum, and the moonwort,Botrychmm Luitaria, are the only British representatives of the class,which comprises only a very small number of species. None are of anyeconomical value.) Class X. Rhizocarpece, The Rhizocarpeae are plants floating

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