:yZ MUSCINE/E. 



GROUP III. 



MUSCINEyE. 



The Hepaticse and Mosses, which are comprised under the term IMuscinese, are 

 distinguished by a sharply defined Alternation of Generations. From the germinat- 

 ing 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 

 (the Pro-embryo or Protonema), 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 fertihsation — 

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

 tion of asexual spores. Without being organically united to the previous generation, 

 this structure is nevertheless nourished by it, and appears, when observed externally, 

 simply as its fruit ; it is hence called indifferently Fruit or Sporangium. 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 Sporogoniiim. 



The Sexual Gefieratio7i of Muscineae which is produced directly from the spore 

 or with the intervention of a pro-embryo, is either a flat leafless thallus, as in 

 many Hepaticse, 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 structure 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 Hmited to only a few weeks or months ; in most it may 

 be termed 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 pro-embryos (in IMosses), &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 IMosses 

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

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



^ From the great similarity of the true leafless thallus of some Hepaticas 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). 



