442 VASCULAR CRYPTOGAMS. 



(c) AsplenieaR. The sori are unilateral on the course of the veins, and are covered 

 by a lateral indusium, or rarely without any ; or they extend at their apex over the 

 back of the veins, and are covered by an indusium springing from it ; or they occupy 

 special anastomosing branches of the veins, and are unilateral and covered by an indusium 

 free on the side of the vein. {Asplenium, Scolopendrium.) 



(d) Aspidiex. The sori are dorsal on the veins, covered with an indusium, or ter- 

 minal and without indusium. {Aspidium.) 



(e) Dwvalliex. The sori are terminal on a vein or at a fork, and are furnished with 

 an indusium ; or are placed on an intramarginal anastomosing bend of the veins, and 

 covered with a cup-shaped indusium, free at the outer margin. {Daruallia, Nephrolepis.) 



(f) Pteridex. The sori are continuous along the margin of the leaf, and are covered 

 by a false indusium. {PteriSf Adiantum^ Blechnum.) 



Order III. RHIZ0CARPE^^ 



The Sexual Generation (Oophore) of Rhizocarps is developed from spores 

 of two different kinds ; the smaller spores {niicrospores) produce antherozoids, 

 and are therefore male ; the larger spores {macrospores), which exceed the smaller 

 kind several hundred times in size, produce a small prothallium, which never 

 separates from them, and forms one or several archegonia; the macrospores may 

 therefore be considered to be female. 



The development of the antherozoids is preceded by the formation of a very 

 rudimentary Male Prothallium. In the genus Salvinia the microspores lie imbedded 

 in a mass of granular hardened mucilage (as they do also in Azolla, in which plant 

 their germination is not known), which fills up the whole of the microsporangium ; 

 they do not escape, but the endospore of each of them grows out into a tube 

 which pierces the mucilage and the wall of the sporangium and forms a septum at 

 its curved end (Fig. 309, A and B). The terminal cell of the tube thus produced 

 is again divided by an oblique wall, after which the protoplasm contracts in the two 

 cells (which Pringsheim together calls the antheridium), and splits up by repeated 

 bipartition into four roundish primordial cells, each of which forms an antherozoid. 

 In addition a small portion of the contents remains inactive in each of the two 

 cells. The antheridial cells burst by transverse slits to allow the escape of the 

 antherozoids. The spirally- coiled antherozoid is still enclosed for a time in its 



•^ G. W. Bischoff, Die Rhizocarpeen u. Lycopodiaceen (Niirnberg 1828). — Hofmeister, Vergleich. 

 Untersuch. 1851, p, 103. — [On the Germination, Development, and Fructification of the Higher 

 Cryptogams, Ray Soc. 1862, pp. 318-335.] — Ditto, Ueber die Keimung der Salvinia natans (Abhand. 

 der konigl. Sachs, Gesellsch. der Wissensch. 1857, p. 665). — Pringsheim, Zur Morphologie der Sal- 

 vinia natans (Jahrb. fiir wissensch. Bot. vol. HI. 1863). — J. Hanstein, Ueber eine neuholliindische 

 Marsilia (Monatsber. der Berliner Akad. 1862, Ann. des Sci. Nat, 4th series, vol. XX, 1863, PP- ^49- 

 166). — Ditto, Befruchtung u. Entwickelung der GdXX.\xng Marsilia (Jahrb. fiir wissensch. Bot. vol. IV, 

 1865). — Ditto, Pilularise globuliferse generatio, cum Marsilia comparata (Bonn 1866), — Nageli u. 

 Leitgeb, Ueber Entstehung u. Wachsthum der Wurzeln bei den Gefasskryptogamen (Berichte der 

 bayer. Akad. der Wissensch. 1866, Dec. 15, and Nageli's Beitiage zur wissensch, Bot, vol. IV. 1867). 

 — Millardet, Le Prothallium male des Cryptogames vasculaires (Strasbourg 1869), — A. Braun, 

 Ueber Marsilia u, Pilularia (Monatsber, der konigl. Akad, der Wissensch, Berlin, Aug, 1870). — 

 E. Russow, Histologic u. Entwickelung der Sporenfrucht von Marsilia (Dorpat 187 1). — Strasburger, 

 Ueber Azolla (Jena 1873). — Juranyi, Uber die Entwickelung der Sporangien und Sporen von Salvinia 

 natans (Berlin 1873), — [Arcangeli, Sulla Pilidaria globulifera e suUa Salvinia natans; Nuov. Giorn, 

 Bot. Ital. 1876.] 



