144 SECOND GROUP.—MUSCINEAE. 



rows of leaves ; this vegetative body is usually spread out on the ground or some 

 other substratum and clings closely to it, and where the stem grows free, the tendency 

 to the formation of an upper and an under side is still plainly expressed ; the growth 

 is therefore always decidedly dorsiventral, except in the thalloid genus Riella and the 

 foliose genus Haphmilrium. The second generation, the sporogonium, remains 

 inclosed till the spores are mature in the calyptra, which is in most cases at length 

 ruptured at the apex and remains as an open sheath at the base of the sporogonium, 

 while the free capsule opens longitudinally above it to discharge the spores. The 

 spore-mother-cells are formed from all the cells inside the single layer which forms 

 the wall of the capsule ; or certain cells lying among and between the others are 

 developed as elaters, and this is the more common case. 



2. Musci or Mosses. The sexual generation is developed from the spore with 

 the intervention of a protonema, which is usually formed of branched rows of cells, 

 but is sometimes a flat expansion, and often continues to live and grow independently 

 for a considerable time, even after it has produced leafy moss-stems from lateral buds. 

 The vegetative body is never a thallus, but always a filiform stem with two, three, or 

 four rows of leaves, usually without distinct bilaterality, and monopodially never 

 dichotomously branched. The second generation, the sporogonium, only begins its 

 development in the calyptra, which is then usually torn away below at the vaginula, 

 and is carried up as a cap on the top of the sporogonium ; the capsule which now 

 becomes fully developed produces the spores from an internal layer of tissue, while a 

 large central mass of tissue remains sterile and constitutes the columella, which dis- 

 appears in the ripe capsule ; in Archidhivi there is no appearance of a columella. 

 The wall of the capsule has a strongly developed epidermis, the upper portion of 

 which separates as a lid {opcritdum') from the lower portion, the urn or thcca, in order 

 to release the spores. 



HEPATICAE'. 



Except in two genera, Riella and Haplomitriwn, the vegetative body in the 

 Hepaticae is always decidedly dorsiventral, its free side, which is turned to the light, 

 having a different organisation from that of the shaded side which is turned towards 

 the substratum, and often clings closely to it. 



In most families and genera the vegetative body is a broad flat or crisped plate 

 of tissue, varying from a few millimetres to several centimetres in length. In the 

 simplest case it is a thallus with no leaves or leaf-like appendages, as in Anthoceros, 



' Mirbel, Recherches anat. et phys. sur la Marchantia polymorphc (Mem. de I'Acad. d. sc. de 

 rinstit. de France, T. XIII. 1835). — Bischoff, Benieik. u. d. Lebenmoose, vorz. u. d. Gruppen d. 

 Marchantiaceen n. Riccien (Nova acta Akad. Leop. Car. 1835, Vol- XVI. p. 2\ — Gottsche, Ueber 

 Haplomitrium Hookeri (Nova Acta, Vol. XX. pars 2). — Nageli in Zeitschrift fur wiss. Bol. — 

 Gottsche, Lindenberg u. Esenbeck, Synopsis Hepaticarum, Hamburg, 1844. — Hofmeister, Vergl. 

 Unters. 185 1. — Kny, Entw. d. laubigen Lebermoose (Jahrb. f. wiss. Bot. IV. p. 64), und Entw. d. 

 Riccien (Jahrb. Bd.v. p. 359). — Thuret in Ann. d. sc. nat. 1851,7. XVI. (Antheridien).— Strasburger, 

 Geschlechtsorgane u. Befruchtung bei Ma>-chantia (Jahrb. f. wiss. Bot. VII. p. 409). — Janczewski, 

 Vergl. Unters. ii. d. Entwicklungsgesch. d. Archegoniums (Bot. Zeit. 1872, Nr. 21 ff.) — Leitgeb, 

 Unters. u. d. Lebermoose, Heft 1-6, 1874-1881.— Kienitz-Gerloff, Vergl. Unters. ii. d. Entwick- 

 lungsgesch. d. Lebermoossporog. (Bot. Zeit. 1874 and 1875^ — [Vochting, Ueber d. Regeneration d. 

 Marchantieen (Pringsh. Jahrb. xvi. 1885).] 



