226 MOSSES AND FERNS chap. 



is extremely large, and complicated in structure, and essentially 

 like that of the other stegocarpous Mosses; secondly, Bux- 

 baumia has been shown by Haberlandt ((4), p. 480) to be 

 distinctly suprophytic in its habits, and the extreme reduction 

 of the assimilative tissue of the gametophyte is quite readily 

 explicable from this cause. 



Fossil Muscine^ 



The remains of Muscinese in a fossil condition are exceed- 

 ingly scanty ; so much so indeed as to practically throw no light 

 upon the question of their origin and affinities, as nearly all of 

 the forms discovered belong to the later formations, and are 

 either identical with living species or closely allied forms. No 

 doubt the great delicacy of the tissues of most of them, espe- 

 cially the Hepaticse, accounts in great measure for their absence 

 from the earlier geological formations. 



The Affinities of the Musci 



It is perfectly evident that the Mosses as a whole form a 

 very clearly defined class, and that their relationship with other 

 forms is at best a somewhat remote one. Sphagnum, however, 

 certainly shows significant peculiarities that point to a connec- 

 tion between this genus, at least, and the Hepaticse. It will be 

 remembered that the protonema of Sphagnum is a large flat 

 thallus, and not filamentous, as in most Bryales. It it note- 

 worthy, however, that from the margin of this flat thallus later 

 filamentous branches grow out which are apparently identical 

 in structure with the ordinary protonemal filaments of the 

 Bryales. In Andrecea similar flat thalloid protonemata occur, 

 but not so largely developed as in Sphagnum, and finally in 

 Tetraphis a similar condition of affairs is met with. As this 

 occurs only among the lower members of the Moss series, the 

 question naturally arises, does this have any phylogenetic mean- 

 ing ? While it is impossible to answer this question positively, 

 it at any rate seems probable that it has a significance, and 

 means that the protonema has been derived from a thalloid 

 form related to some thallose Liverwort, and that by the sup- 

 pression of the thalloid portion, as the leafy gametophore 

 became more and more prominent, the filamentous branches. 



