342 MUSCINEM, 



GROUP II. 

 MUSCINE^. 



The Liverworts (Hepaticse) and Mosses (Musci), which are comprised under 

 the term Muscineae, are distinguished by a sharply-defined Alternation of Generations. 

 From the germinating spore is developed either immediately a sexual generation 

 rich in chlorophyll and self-supporting (as in most Hepaticae), or a confervoid 

 thallus is first formed {Protonevia), out of which the sexual generation grows as 

 a lateral shoot (as in some Hepaticae and all Mosses). In the female sexual organ 

 of this first generation there arises, as a new generation — the result of fertilisation — 

 a structure of an entirely different form, which is destined exclusively for the 

 asexual production of spores. Without being organically united to the previous 

 generation, this structure is nevertheless nourished by it, and appears, when ob- 

 served externally, simply as its fruit, like the smaller fructifications of the Thallo- 

 phytes. Since however it is an organism of an altogether peculiar kind, it may 

 be desirable to give it a special name, which shall at once exclude any false analogy*; 

 I propose therefore to call it the Sporogonium. 



The Sexual Generation (Oophore) of Muscineae which is produced directly from 

 the spore or with the intervention of a protonema, is either a flat leafless thallus, 

 as in many Hepaticae, or a slender leafy stem, often much branched. In both cases, 

 which are united by gradual transitional forms ^, a number of root-hairs are usually 

 formed, which fix the thallus or the stem to the substratum. In some cases this 

 vegetative body scarcely attains a length of i mm., but in others as much as 

 from lo to 30 cm. or even more, and ramifies copiously. In some of the smallest 

 forms its term of life is limited to only a few weeks or months ; in most it may 

 be said to be unlimited, since the thallus or the leaf-bearing stem continually grows 

 at its apex or by a process of renewal (Innovation), while the oldest parts die off" 

 behind. In this manner the branches become finally independent plants ; and this, 

 as well as the multiplication by gemmae, stolons, detached buds, the transformation 

 of hairs into protonema (in Mosses), &c., serves not only to increase enormously 

 the number of individuals formed by the asexual method, but is also the immediate 

 cause of the social or cespitose mode of growth of these plants. Many Mosses 

 in particular, even those which only rarely fructify, may in this manner form dense 

 masses extending over considerable areas (as Sphagnum, Hypnum, Mnium, &c.). 



^ It is incorrect, for instance, to regard the ' fruit ' of a Moss as the morphological equivalent of 

 the sporangium of a Rhizocarp or of the fruit of a Phanerogam. 



' From the great similarity of the true leafless thallus of some Hepaticse to the thalloid stems 

 of others furnished with leaves on the under side, it will be convenient to use the term ' thalloid 

 forms' for both ; the term including both a true thallus (e. g. Anthoceros) and also a thalloid stem 

 (as in Marchantia). 



