81 
however, omits the species from Greenland and other parts of 
Arctic America, which have not yet been detected farther to the 
southward. These species, which are known to us through the 
researches of C. Jensen, Bryhn, and others, number about 24. If 
these and a couple of other species described since January I are 
added, the total number known from North America north of 
Mexico is 382, an increase of 150 since Underwood published his 
catalogue. The latest estimate of the number occurring in New 
England is 169, more than twice the number given by Underwood. 
This increase in number is partly due to new explorations and 
partly to a more critical study of certain difficult genera. The 
not previously been studied, such, for example, as Yukon, the 
Lake Superior district, and subtropical Florida, but also in regions 
where our knowledge was presumably more complete. Even in 
eastern North America new species are constantly coming to 
light, and seven New England species were detected for the 
first time during the past year. It will doubtless be a long time 
before knowledge of the American Hepaticae can approach in 
thoroughness that of the European countries. 
In comparing our species with those of other regions a very 
striking resemblance becomes apparent between our flora and 
that of Europe. In fact over 200 of our species (223) grow also 
in Europe and it is probable that this number will be increased 
as time goes on. The resemblance is especially great when 
northern species are considered and the number of species which 
grow north of the United States and are not found in Europe is 
very small indeed. In fact, as Underwood noted long ago, the 
Hepaticae of the whole circumpolar region extending across 
Europe, Asia and North America are exceedingly uniform. 
When we consider the species of the southern United States 
the diversity becomes more and more marked due largely to the 
fact that our austral flora contains many tropical elements, some 
of which are known only from peninsular Florida, while others 
extend much farther northward. 
en we go south into Mexico and Central America and 
penetrate also the islands of the Caribbean Sea, the character of 
