The Distribution of the Hepaticce. 205 
Brycphytes is too scanty to be of much value in determining the 
geological history of the group, although what little evidence is 
available is entirely in harmony with the assumption of their 
primitive character. The arguments based upon comparative 
morphology are sufficiently familiar and have been recently 
summarized by the writer (Mosses and Ferns—2nd Edition, Chap. 
XV.); they need not be repeated here. There is, however, a point 
that has not been considered as fully as it might have been, and the 
present paper is an attempt to present this, since it seems to throw a 
great deal of light upon the subject of the antiquity of the Bryo- 
phytes. The point in question is the present geographical distri¬ 
bution of the Bryophytes, especially of the Hepaticae. 
That a study of the present distribution of any group of 
organisms is one of the most important means of determining their 
relative antiquity is generally recognized. Of course there are 
many factors to be considered, and great care must be exercised 
before it is safe to make wide generalizations. Most important of 
all, perhaps, especially in dealing with very wide-spread forms, is 
the question of the means of distribution in very recent times, and 
especially the part that man has played, voluntarily or otherwise, in 
the distribution of many species. 
Studies on geographical distribution have concerned themselves 
largely with the vascular plants, and there are not many critical 
studies of the distribution of Thallophytes and Bryophytes. It has 
been generally assumed that most of these forms are old types, and 
their wide distribution has been accepted as a matter of course. It 
has also been rather taken for granted that the lightness and small 
size of the spores of the Bryophytes and Pteridophytes make the 
rapid dissimination of these plants an easy matter. This latter 
point, however, will be found not to apply to many of the Liverworts, 
whose spores are frequently adapted to immediate germination and 
are not fitted to survive a long journey. Hence the wide distribution 
of many Hepaticae must be explained on other grounds than that of 
rapid distribution by means of the spores. 
Although practically nothing is known of the early geological 
history of the simpler green Algae, it is very generally agreed that 
they are very ancient forms. The cosmopolitan character of most 
genera and of many species point to this, even if the evidence 
furnished by comparative morphology were ignored. The positive 
evidence that forms closely allied to many living calcareous Siphoneae 
lived in early palaeozoic times, makes it extremely probable that the 
