;io 



MOSSES AND FERNS chap. 



in Anthoceros. It is true that the sporogonium ahvays remains 

 to some extent parasitic upon the gametophyte, but this 

 parasitism is very slight in Anthoceros, where the formation of a 

 root would make the sporogonium quite self-supporting. This 

 increase in the vegetative tissues of the sporophyte is at the 

 ■expense of the sporogenous tissue, which becomes more and 

 more subordinated to the assimilative and conductive tissue of 

 the sporogonium, as is seen in the Bryineae among the Mosses, 

 and in Anthoceros. 



In most of the Liverworts the sterile tissues of the sporo- 

 gonium are mainly concerned with the protection and dissemin- 

 ation of the spores. Only the foot, usually, can be properly 

 considered as an organ concerned in the nourishment of the 

 growing embryo. The seta, capsule wall, and elaters are 

 merely adaptations for facilitating the dispersal of the ripe 

 spores. In all of these, except the Anthoceroteae, the whole of 

 the central tissue of the capsule constitutes the archesporium, 

 all of whose cells are devoted to the formation of spores or 

 elaters. In the Anthoceroteae, however, the origin of the arche- 

 sporium is quite different, and it arises not from the central cells, 

 but by a secondary division of the parietal ones. As yet there 

 is no clear evidence of a direct connection with either of the 

 other series of the Hepaticae, and it is a question whether the 

 Anthoceroteae ought not to form a group co-ordinate with all 

 the other Liverworts on the one hand, and the Mosses on the 

 other. It is possible that the axial bundle of sterile cells found 

 in the capsule of Pellia and Aneura may be homologous with 

 the columella of the Anthoceroteae, and the latter therefore to 

 be considered as derived directly from some simple form among 

 the anacrogynous Jungermanniaceae ; but as the sporogonium 

 in all the Anthoceroteae that have been thoroughly investigated 

 shows absolutely the same type of structure, and in no case a 

 secondary formation of the columella, this is hardly probable. 

 In the higher Anthoceroteae, also, the wall of the capsule, 

 instead of simply serving for the protection of the spores, 

 becomes a massive spongy green tissue communicating with 

 the atmosphere by means of perfectly -developed stomata of 

 exactly the same type as those of the vascular plants. This 

 similarity in the assimilative system, together with the basal 

 growth of the sporophyte and the central strand of conductive 

 tissue, has of course suggested a relationship with the vascular 



