DIVISION II. 



MUSCINE^ (MOSSES). 



In this Division a well-marked alternation of generations is to be 

 found. The development of the first or sexual generation (gameto- 

 pliyte), 1 which bears the sexual organs, antheridia and archegonia, 

 commences with the germination of the spore, and consists, in the 

 Liverworts, of a thallus, but in the true Mosses of a filamentous 

 protonema, from which the Moss-plant arises as a lateral bud. 

 The second or asexual generation (sporophyte), developed from the 

 fertilised oosphere, consists of a sporangium and stalk. 



The sexual generation, the gametophyte. The protonema 

 in the Liverwoi-ts is very insignificant, and not always very sharply 

 demarcated from the more highly developed parts of the nutritive 

 system. In the true Mosses the protoiiema is well-developed, and 

 consists of a branched, alga-like filament of cells, the dividing 

 cell-walls being always placed obliquely. In the parts exposed to 

 the light it is green, but colourless or brownish in those parts 

 which are underground (Fig. 186). The protonema is considered 

 to be a lower form of the stem, and grows in the same manner 

 by means of an apical cell ; at its apex it may directly develope 

 into a leaf-bearing stem, or these arise from it as lateral branches 

 (Fig. 186 it). 



The more highly differentiated part of the vegetative system, 

 the " Moss-plant," which is thus developed from the protonema, 

 is in the " thalloid " Liverworts generally a dichotomously- 

 branched thallus without any trace of leaf-structures (Fig. 

 194) ; in Marchantia (Fig. 197) and others, scale-like leaves 

 (amphigastria) are found on the under surface. The higher 

 Liverworts and the Leafy-Mosses are differentiated into a fila- 

 mentous, ramified stem with distinct leaves arranged in a definite 

 manner, resembling the stem and leaves of the higher plants (Figs. 

 186, 195, 200). 



1 Formerly termed oophyte. 

 181 



