. Botany for high schools and colleges. Botany. 376 BOTANY. spore cavity (Fi<^. 2G1, C, r). By the contraction of this ring the ripe sporauginni is ruptured and the spores set free. In some cases, instead of forming a ring, tlie elastic cells are arranged as a group at one side or end of the sporangium. Six families or suborders of the Ferns may be distinguished, if we take into consideration the characters derived from the asexual genera- tion. They have been arranged as follows : * 1. Oleicheniacem.—Sporangia sessile, splitting vertically, furnished with a complete horizontal ring. Sori c
. Botany for high schools and colleges. Botany. 376 BOTANY. spore cavity (Fi<^. 2G1, C, r). By the contraction of this ring the ripe sporauginni is ruptured and the spores set free. In some cases, instead of forming a ring, tlie elastic cells are arranged as a group at one side or end of the sporangium. Six families or suborders of the Ferns may be distinguished, if we take into consideration the characters derived from the asexual genera- tion. They have been arranged as follows : * 1. Oleicheniacem.—Sporangia sessile, splitting vertically, furnished with a complete horizontal ring. Sori composed of very few sporangia ; receptacle not elevated (Fig. 263). Fronds with very distinct dichot- omous branching. Genera two {Platyzoma and Oleichenia); species thirty, mostly confined to the southern hemisphere. 2. Hymenophyllaceoi.— Sporangia sessile, split- ting vertically, furnish- ed with a complete horizontal ring. Sori composed of numerous sporangia inserted on a long filiform receptacle (Fig. 264). Leaves of filmy texture (usually of a single layer of cells), with pinnate branching. Genera two {Hymeno- phyllum and Tridioma- nes); species 150 to 200, mostly confined to the tropics. 3. Gyatheacem. — Spo- rangia nearly sessile, splitting Fig. 262.—Development of the spores of Aspidium Filix-mas. /., a mother-cell containing a nucleus; //., the same after the absorption ot the nucleus ; III., the mother-cell, with two large clear nuclei— sometimes a line of stparation is evident, as in the figure ; IV., the mother-cell, with four clear nuclei, w^ich appear after the absorption of the two in ///.; F., the four daughter-crlls (young spores) M'hich form from IV.; VI, VII., VIII, different relative positions of the developing spores ; IX., the perfect spore, x 550.—After Sachs. * The characters and arrangement of the suborders of ferns are taken from the article " Ferns," by W. T. T. Dyer and J. G. Baker, in the " Encyclopaedia Bri
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