MUSCINEJE. 183 



stage of development. This strand contains elements for convey- 

 ing water as well as sieve-tubes. Stomata are entirely wanting in. 

 the sexual generation of the Leafy-Mosses ; they are found in a 

 few Liverworts (Marchantia) ^ but their structure is not the same 

 as in the higher plants. 



VEGETATIVE REPRODUCTION takes place by gemmae or buds which 

 arise on the protenema, the rhizoids, the thallus, or the shoots, and 

 become detached from the mother-plant ; or else the protonema 

 and the older parts of the plant simply die off, and their branches 

 thus become independent plants. This well-developed vegetative 

 reproduction explains why so many Mosses grow gregariously. 

 In certain Marchantiacea? special cupules, in which gemmre are 

 developed, are found on the surface of the thallus (Fig. 197 J,s-,*). 



FIG. 137. Marchantia polymorpha : FIG. 188. Spermatozoids. 



a mature untheridium. 



Again, protonema may also arise from the leaves, and thus the 

 leaves may act as reproductive bodies. Certain Mosses nearly 

 always reproduce vegetatively, and in these species the oospheres 

 are seldom fertilised. 



The first generation bears the SEXUAL ORGANS ; both kinds are 

 found either on the same plant (monoecious), or on separate plants 

 (dioecious). In the thalloid Liverworts they are often situated on 

 the apex of small stems (gametophores'), springing from the surface 

 of the thallus. In the Leafy- Liverworts and true Mosses the leaves 

 which enclose the sexual organs often assume a peculiar shape, and 

 are arranged more closely than the other leaves to form the so-called 

 " Moss-flower." The male sexual organs are called antheridia. 

 They are stalked, spheroid, club- or egg-shaped bodies whose 

 walls are formed of one layer of cells (Fig. 187), enclosing a mass 

 of minute cubical cells, each one of which is a mother-cell of 



