The Distribution of the Hepaticce. 
209 
distributed between tropical America and New Zealand. Dumor- 
tiera and Dendroceros are widely distributed throughout the tropics, 
and the former extends beyond the tropics into the warm temperate 
zone. 
Only a small number of species are of limited range, and these 
are often monotypic. Of these monotypic forms Wiesnerella 
Javanica, Schiff. is as yet known only from Mount Gedeh in Java, 
and Geothallus tuberosus Campbell, has only been collected near 
San Diego in Southern California. It is not safe to assume that 
these species are really as restricted in their range as they now 
appear to be. It is highly probable that they will be found at other 
places, as has been the case with Treubin insignis, which for a long 
time was known only from Mount Gedeh in Java, but has since been 
found by its discoverer, Goebel, in New Zealand. A similar case is 
that of the genus Riella, which until recently was known only from 
Southern Europe and Northern Africa, but which is now known to 
occur in Turkestan, the Canary Islands, and in at least two localites 
in the United States. (Howe & Underwood, The Genus Riella, 
etc., Bull. Torrey Bot. Club, 30: p. 214, 1903). 
The most obvious fact that presents itself from a study of the 
distribution of the Hepaticae is the small number of genera and 
their wide distribution, this being especially the case among those 
forms which for other reasons are supposed to be the most ancient. 
The great preponderance of the foliose Jungermanniales is entirely 
in harmony with the conclusion of the morphologists that they are 
the most modern of the Liverworts. It is inconceivable that a 
recently developed group of plants could have spread over the world 
as the simpler types of Hepaticce have done, with so little modifi¬ 
cation, unless there were some extraordinary means of rapid 
dissemination. There certainly is very little evidence that this is 
the case with the Hepaticae. Let us consider the little group of the 
Anacrogynae, or thallose Jungermanniaceae. This group comprises 
less than 300 species, distributed among about twenty genera. Of 
the latter, more than three-fourths are either cosmopolitan, or at 
any rate of very wide distribution. It is only necessary to contrast 
these figures with those of such an evidently modern group of plants 
as the family Orchidaceae, or Compositae. Out of over 400 genera 
and 5,000—10,000 species of the former family, probably not a 
single one is cosmopolitan, and the great majority, both of genera 
and species, are of comparatively narrow range. 
A number of families of Angiosperms, which to judge from 
