INTRODUCTION. 9 
Rockcastle counties, which is only occasionally met with 
so far westward and southward.* 
Ferns are quite generally distributed over the surface of 
the globe. In the tropics they form a very characteristic 
feature of the vegetation. They are found in Greenland, 
in Iceland, at the North Cape, and throughout all tem- 
perate regions; but it is in the tropics that they attain 
their maximum size. Here, only, they assume a tree-like 
form. The horticultural department of the United States 
Centennial Exposition afforded American botanists a fine 
opportunity for the study of this curious, palm-like plant. 
Speaking of the Tree Fern, Darwin says: “In some of the 
dampest ravines Tree Ferns flourish in an extraordinary 
manner; I saw one which must have been twenty feet high 
to the base of the fronds, and was in girth exactly six feet. 
The fronds, forming the most elegant parasols, produced a 
gloomy shade, like that of the first hour of night.” (Voy- 
age of a Naturalist, Am. Ed., page 144.) In the early ages 
of the earth’s history the Tree Fern must have been widely 
distributed, as its remains form a striking feature of some > 
*Mr. J. H. Redfield, of Philadelphia, has made a valuable con- 
tribution to the ‘‘ Geographical Distribution of the Ferns of North 
America,” in which the ferns inhabiting this country are arranged in 
six geographical divisions: I. COSMOPOLITAN: Widely distributed 
over the globe, in both the temperate and tropical regions. IT. 
BOREAL: Inhabiting (with a few exceptions) the northern portion 
of the United States, British America, and Greenland. III. Appa- 
LACHIAN: Extending throughout the mountain and hilly regions 
of the states east of the Mississippi. IV. Paciric: Extending along 
the western border of the continent, from Alaska to California, and 
appearing in the Rocky Mountain region. V. NEw Mexico: Inhab- 
iting the Central Mountain regions of New Mexico and Colorado. 
VI. Tropica: Inhabiting the border of the Gulf of Mexico, most 
of the species extending into the West Indies and Tropical America. 
(See Bulletin of the Torrey Botanical Club, vol. vi, page 1.) 
