MUSCINE^E 135 



filamentous structure, the prothallus or protoneme, on which the leafy 

 plant containing chlorophyll arises as a lateral shoot. The Muscinese 

 present, therefore, an illustration of the phenomenon of alternation of 

 generations ; the sexual generation which intervenes between germina- 

 tion and impregnation, or oophyte, consisting of the protoneme (when 

 present), the leafy (or thalloid) plant, together with the sexual organs ; 

 the non-sexual generation intervening between impregnation and ger- 

 mination, or sporophyte, consisting of the sporogone only with its 

 spores. 



The Muscinese are divided into two well-marked families, the Musci 

 or Mosses, and Hepaticce. or Liverworts. In the Musci the immediate 

 result of the germination of the spore is always a protoneme consisting 

 erf branched rows of green or colourless cells, and often growing for a 

 considerable time independently, even after it has produced leafy stems 

 by lateral budding. The vegetative structure is always cormophytic, 

 and consists of a filiform stem furnished with two, three, or four rows of 

 leaves, not exhibiting any distinct bilateral structure, and branching 

 monopodially, never dichotomously. The sporogone is only for a time 

 enclosed in the calypter, which is usually eventually ruptured below, the 

 lower portion developing into the vagine, while the upper part is elevated 

 above the apex of the sporogone in the form of a cap. The spore- 

 mother-cells are produced from one or more special layers of tissue 

 within the sporange, the archespore, while the axial mass develops into 

 a solid columel. The uppermost portion of the wall of the sporange 

 forms a lid or opercule, which usually becomes detached from the lower 

 portion, to which the term theca or sporange specially belongs, to allow 

 the escape of the spores. The outermost layer of cells of the wall of 

 the sporange is more or less completely differentiated into an epiderm, 

 which is frequently penetrated by stomates. When the opercule is 

 removed, the rim of the sporange is either quite smooth, when it is 

 termed gymnostomous, or the edge is furnished with delicate hair-like 

 appendages, constituting the peristome, arranged in a single row or fre- 

 quently in two, when they are called respectively teeth and cilia, the 

 former constituting the outer, the latter the inner row. The number of 

 both teeth and cilia is always a multiple of four, or more correctly speak- 

 ing, a ' power ' of two. In the Hepaticae the protoneme is either scantily 

 developed or is altogether suppressed. The rest of the sexual generation 

 consists either of a flat dichotomously branched thallus or thalloid stem, 

 or of a slender stalk furnished with two or three rows of leaves. In the 

 division into Foliose and Thalloid or Frondose forms, the Hepaticse 

 therefore present the transition from Cormophytes to Thallophytes. The 

 mode of growth is always distinctly bilateral ; the thalloid forms cling 



