22,8 THIRD GROUP. VASCULAR CRYPTOGAMS. 



an intramarginal anastomosing bend of the veins and covered by a cup-shaped 

 indusium which is free at the outer margin (Davallia^ Nephrolepis}. 



4. GLEICHENIACEAE. Sporangia without stalks, usually three or four together in a 

 sorus, without indusium on the dorsal surface of ordinary leaves, with a complete 

 transverse annulus in the centre of the sporangium and longitudinal dehiscence. Stem 

 a slender creeping rhizome ; leaves with peculiar innovation of the lamina. 



5. OSMUNDACEAE. In Osmunda the sporangia are arranged in panicles and placed 

 on the laciniae of leaves which have no mesophyll ; in Todea the fertile leaves resemble 

 the sterile. The sporangia are on short stalks and of an unsymmetrical roundish 

 form ; they have on one side of their apex a group of peculiarly shaped cells, and open 

 by a longitudinal fissure on the other. The short stem, which is very densely covered 

 with roots, gives rise to similar lateral shoots. The structure of the stem which has 

 been described above is remarkable ; the course of the vascular bundles resembles that 

 in the Coniferae and Dicotyledons. 



6. SCHIZAEACEAE. The laciniae which bear the sporangia are arranged in spikes 

 or panicles, except in Mohria, where the sporangia are on the under surface of the 

 leaf near the margin which is turned back over them, the indusium being a con- 

 tinuation of the leaf margin; in Schizaea&n&Lygodium the sporangia are in two rows on 

 the under side of very reduced laciniae, and in Lygodiwn each sporangium is covered 

 by a pocket-shaped indusium : in Aneimia the two lowest branches of the lamina 

 have no mesophyll and form panicles with long stalks, on the ultimate ramifications of 

 which the sporangia arise in acropetal succession from the marginal cells of the 

 segment of the leaf. In the other Schizaeaceae also the sporangia proceed from mar- 

 ginal cells, and subsequently appear displaced on the under side of the leaf. Schizaea 

 has bilateral spores ; in the other genera they are roundish-tetrahedral. The ovoid 

 or pear-shaped sporangia are sessile ; their apex is occupied by a cap-like zone of 

 peculiarly formed cells ; the dehiscence is longitudinal. The stem, except in Aneimia 

 and Mohria, appears occasionally to remain unbranched, and is very feebly developed; 

 the leaf-stalks have only one vascular bundle ; the leaves of Lygodium resemble a 

 climbing stem. 



2. HETEROSPOROUS FILICINEAE OR HYDROPTERIDEAE 1 . 



The heterosporous Filicineae, once grouped together under the highly unsuitable 

 name of Rhizocarpae, fall naturally into two families, one of which, the Salviniaceae, 

 comes very near to the homosporous Ferns, while the other, the Marsiliaceae, exhibits 

 a special type of its own in the formation of its sporocarps. Although the two 

 families therefore are derived from different original stocks among the homosporous 



1 Bischoff, Die Rhizokarpeen u. Lycopodiaceen (Nurnberg, 1828). Hofmeister, Vgl. Unters. 

 1851, p. 103 ; Id. Ueber d. Keimung d. Salvinia natans (Abh. d. Kon. Sachs. Ges. d. Wiss. 1857, 

 p. 665). Pringsheim, Zur Morph. d. Salvinia natans (Jahrb. f. wiss. Bot. iv. 1863). Hanstein, 

 Befruchtung u. Entw. d. Gattung Marsilia (Jahrb. f. wiss. Bot. iv. 1865) ; Id. Pilulariae globuliferae 

 generatio cum Marsilia comparata (Bonn, 1866). Nageli u. Leitgeb, Ueber Entstehung u. 

 Wachsthum d. Wurzeln beid. Gefasskryptogamen in Nageli's Beitr. z. wiss. Bot. iv. 1867. Millardet, 

 Le prothallium male des Cryptogames vasculaires, Strasbourg, 1869. A. Braun, Ueber Marsilia 

 u. Pilularia (Monatsber. d. kgl. Akad. d. Wiss. Berlin, 1870 u. 1872). Russow, Vergl. Unter. 

 Petersburg, 1872. Strasburger, Ueber AzQlla, Jena, 1873. Juranyi, Ueber d. Entw. d. Spo- 

 rangien u. Sporen von Salvinia natans, Berlin, 1873. Arcangeli, Sulla Pilularia e la Salvinia 

 (Nuovo Giornale Bot. Ital. vol. viii. 1876). Leitgeb, Zur Embryologie d. Fame (Akad. d. Wiss. 

 zu Wien, 1878). Prantl, Zur Entwickl. Gesch. d. Prothallium von Salvinia natans (Bot. Zeit. 1879, 

 p. 425). Sadebeck, Keimung von Marsilia-Mikrosporen, loc. cit. [Bower, Comp. Morph. of the 

 leaf in Vase. Crypt and Gymnosp. (Phil. Trans. 1884).] 



