BYLOGRTIN 
OF THE 
ORREY BOTANICAL CLUB. 
ol VI. New York, January, 1875. [No 1. 
§ 1. Geographical Distribution of the Ferns of North America, 
By Jonn H. Reprierp. 
For many reasons, writers upon the Flora of North America 
have found it convenient and useful to limit their province to that 
of the continent lying north of Mexico, excluding also the 
est Indian Islands. In considering the distribution of the Ferns 
of North America a similar limitation will be followed, which will 
exclude a large number of tropical forms that can be better stu- 
died in connexion with South American or Caribbean geography. 
As Ferns are for the most part very dependent upon shade and 
moisture, their distribution over the continent will be largely deter- 
mined by the rain-fall of the different portions; and the same con- 
ditions which locate the forest regions, will show us where we may 
xpect to find the largest number of species and the greatest devel- 
opment in number and luxuriance of individuals. And as many 
“species live only in the crevices of rocks, or root only in rock-loving 
“mosses, they find in the rugged cliffs of mountain sides all the 
“necessary conditions, 
_ So, as we might expect, the eastern portion of the continent— 
traversed from N. E. to 8. W. by the Appalachian range of moun- 
tains which receive and condense the moisture of the winds from 
the Gulf of Mexico and the Atlantic—furnishes the greatest num- 
species belonging to the Caribbean province. These soon disap- 
pear as we go northward, and as we proceed into Canada and the 
British possessions, many of the Alleghanian forms die out, and are 
succeeded by more hardy and cold-enduring species. A few of — 
_ these continue into high arctic latitudes. Passing now westward 
_ beyond the Alleghanian slopes, into the flat, treeless prairies of the 
- Mississippi valley, and still farther, into the arid plains which ex- 
tend to thefoot of the Rocky Mountains, we have a vast region, 
in which the species gradually diminish in number, and finally 
almost entirely disappear. Even in the Rocky Mountains we find 
_tmany of the needed conditions wanting. An atmosphere almost de- 
_ void of moisture through much of the year, and so free from cloud as 
_ to give burning effect to the direct rays of the sun, limits the fern 
_ growth to deep rock clefts and to the valleys of snow-fed streams. 
_A few Boreal and Siberian forms have crept downwards from the 
north, meeting some of the drought-resisting species which have 
made their way from Mexico, | 
_ Beyond the Rocky Mountains, we enter a widespread desert, 
; 
ber of species. Near the Gulf, the moisture of the atmosphere is 
accompanied by sufficient heat to permit theestablishment of many = 
