. Botany for high schools and colleges. Botany. 37(3 BOTANY. spore cavity (Fig. 261, C, r). By the contraction of this ring the ripe sporangium is ruptured and the spores set free. In some cases, instead of forming a ring, the 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. Oleiolieniacem.—Sporangia sessile, splitting vertically, furnished witli a complete horizontal ring. Sori comp
. Botany for high schools and colleges. Botany. 37(3 BOTANY. spore cavity (Fig. 261, C, r). By the contraction of this ring the ripe sporangium is ruptured and the spores set free. In some cases, instead of forming a ring, the 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. Oleiolieniacem.—Sporangia sessile, splitting vertically, furnished witli 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 Gleichenia); species thirty, mostly confined to the southern hemisphere. 2. Hymenophyllaeem.— 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 (Mymeno- phyllum and Trichoma- nes); species 150 to 200, mostly confined to the tropics. 3. Cyafheacem. — Spo- rangia nearly sessile, splitting Fig. 262.—Development of the spores of Aspidivmi Filix^maa. /., a mothur-cell containing a nucleus; //., the same after the absoi'ption of the nucleus ; III., the mother-cell, with two Jarjre clear nuclei— sometimes a line of stparation is evident, as in the figure ; /F., the mother-cell, with four clear nuclei, wnich appear after the absorption of the two in ///.,' K, the four daughter-cells fj'oung spores) which 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 Br
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