MUSCI. 163 



kinds occur in pretty equal proportions. In Preissia the sterile thallus branches 

 dichotomously, but a change takes place when a sexual shoot is formed, the two first 

 bifurcations of a dichotomy being applied to this purpose (in Marchantia one of them 

 continues to grow on as a vegetative shoot) ; then a ventral shoot makes its ap- 

 pearance immediately under the apex, and grows in the direction of the mother-shoot, 

 and in this way the thallus of this genus is formed with its member-like shoots. In 

 Targionia and Sauteria alpina the regular position of the antheridia is on ventral 

 shoots. 



MUSCI 1 . 



The spore produces a confervoid structure, the protonema, on which the 

 Moss-plant proper arises as a lateral shoot with differentiation of stem and leaf; on 

 this plant the sexual organs are formed, the sporogonium proceeds from the oospore 

 in the archegonium, and the spores are formed in it from a small portion of the 

 inner tissue. 



The protonema is in the typical Mosses a tubular outgrowth of the endosporium, 

 which has unlimited power of elongation by apical growth and is divided into cells 

 by obliquely transverse walls inclining in different directions ; the cells are subject to 

 no intercalary divisions but form branches immediately behind the septa, and these 

 are also divided by transverse walls and have usually a limited power of apical growth ; 

 they can in their turn produce branches. The part of the endosporium opposite to the 

 germ-tube may develope into a hyaline rhizoid penetrating into the ground, or it may 

 develope into another germ-tube. The cell-walls of the protonemal filaments are at 

 first colourless, but the primary axes run along the ground or penetrate into it, and 

 then their walls assume a dark colour. The cells that are above the ground form an 

 abundance of chlorophyll-corpuscles ; the protonema therefore feeds by carbon-assimi- 

 lation, and not only attains in many genera a considerable size, covering a surface of 

 from one to several square inches with a turf of closely entangled filaments, but its 

 duration may sometimes be said to be unlimited ; in most Mosses it disappears after 

 it has produced the leafy stems as lateral buds ; but if these remain very small and 

 are short-lived, as in the Phascaceae, Pottia, Physcomitrium and others, the protonema 

 continues in vigorous life after it has produced leafy plants, and even when sporogonia 

 have been formed on them : in such cases we have before us in organic connection 

 at the same time all the three forms of the cycle of development. The Sphagnaceae, 

 Andreaeaceae and Tetraphideae differ from the typical Mosses in the character of their 



1 W. P. Schimper, Recherches anat. et physiol. sur les Mousses, Strassburg, 1848. Lantzius 

 Beninga, Beitr. z. Kenntn. d. Baues d. ausgewachsenen Mooskapsel, insbesondere d. Peristoms (mit 

 prachtigen Abbildungen) (Nova Acta Leopold. 1847). Hofmeister, Vergl. Unters. 1851 ; Id. 

 Berichten d. Kon. Sachs. Ges. d. Wiss. 1854 ; Id. Entw. d. Stempels d. beblatt. Muscineen (Pringsh. 

 Jahrb. iii). linger, Ueber d. anat. Bau d. Moosstammes (Sitz.-Ber. d. Kais. Akad. d. Wiss. Wien, Bd. 

 43, p. 497). K. Miiller, Deutschlands Moose, Halle, 1853. Lorentz, Moosstudien, Leipzig, 1864; Id. 

 Grundlinien zu einer vergl. Anat. d. Laubmoose (Pringsh. Jahrb. f. wiss. Bot. vi. u. Flora 1867). 

 Leitgeb, Wachsthum d. Stammchens von Fontinalis antipyretica u. von Sphagnum, and Entw. d. 

 Antheridien ders. (Sitz.-Ber. d. K. Akad. d. Wiss. Wien, 1868 u. 1869) ; Id. Das Sporogon von 

 Archidium (Sitz.-Ber. d. Akad. 1879). J- Kuhn, Entwicklungsgesch. d. Andreaeaceen, Leipzig, 

 1870 (Mittheil. aus d. Gesammtgebiet d. Bot. von Schenk u. Lurssen, Bd. i). Janczewski, Entw. d. 

 Archegonien (Bot. Zeit. 1872, No. 21 ff.). Kienitz-Gerloff, Unters. u. d. Entw. d. Laubmooskapsel 

 (Bot. Zeit. 1878). [Gobel, Vergl. Entwickgs. d. Pflanzenorgane in Schenck, Handb. d. Bot. III.] 



M 2 



