The structure and development of mosses and ferns (Archegoniatae)

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Identifier: structuredevelop00camp3 (find matches)
Title: The structure and development of mosses and ferns (Archegoniatae)
Year: 1918 (1910s)
Authors: Campbell, Douglas Houghton, 1859-1953
Subjects:
Publisher: New York, Macmillan
Contributing Library: The LuEsther T Mertz Library, the New York Botanical Garden
Digitizing Sponsor: The LuEsther T Mertz Library, the New York Botanical Garden

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s germinate promptly, varying from two or threedays to about a week, depending upon the temperature. Theexospore is ruptured irregularly near one end, and through thisa short colourless papilla protrudes and is shut off by a trans-verse wall (Fig. 173, B). This papilla contains little or nochlorophyll and rapidly lengthens to form the first rhizoid,which undergoes no further divisions. The large green cellalone produces the prothallium. The divisions in the pro-thallial cell vary somewhat, but in the great majority of cases aseries of transverse walls is first formed, and the young pro-thallium (Fig. 173, C) has the form of a short filament.Sooner or later, in normally-developed prothallia, the terminalcell of the row becomes divided by a longitudinal wall, whichmay be straight, but more frequently is oblique and followedby another similar wall in the larger of the two cells, meeting itso as to include a triangular cell, which is the two-sided apical IX FILICINE/E LEPTOSPORANGIAT^ 313
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Fig. 173.—Onoclea struthiopteris. A, B, Germinating spores with the perinium re-moved, X300; C, young prothallium, Xioo; D, E, older prothallia with two-sidedapical cell (x), X300; F, small female prothallium seen from below, X25; G,very young prothallium with the two outer spore-coats, X300; r, primary rhizoid;ar, archegonia; p, perinium; ex, exospore. 314 MOSSES AND FERNS chap, cell of the next phase of the prothalliums growth. Thedivisions up to this point correspond exactly with those ofAneura or Metzgeria, and are also much the same as in Marat-tia, except that in Onoclea the prothallium only in very rarecases assumes the form of a cell mass at first. By the regularly alternating segments of the apical cellthe young prothallium soon assumes a spatulate form, whichbecomes heart-shaped by the rapid growth of the outer cells ofthe young segments, which grow out beyond the apical cell.Sooner or later the single apical cell is replaced by two ormore initials formed from it in the sa

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