14 THE UNCOILING FRONDS. 
coal measures. The presence of great beds of coal in 
lands that are now covered with ice and snow for a large 
part of each year, indicate that they once supported a 
luxuriant fern-flora. The temperature was then, of 
course, much higher. The tree ferns’ descendants still 
retain their love for warmth, shade and moisture, and 
perhaps are still as abundant upon tropical islands as 
ever, but there is scarcely a spot on the globe without 
one or more species, unless it is an absolute desert. 
Nearly all ferns are perennial, although individual 
fronds seldom live more than a year. Many, even ina 
climate like that of Canada, are evergreen. The tree- 
fern with an erect trunk and a tuft of fronds at the sum- 
mit is probably the typical form. Our common species 
are supposed to be without trunks because they do not 
rise above the earth but one has only to dig up the 
nearest species to find that if it has not a true trunk, it 
has what is equivalent to one. This is usually a hori- 
zontal axis, bearing the crown of fronds at one end and 
giving off roots especially from the under surface. It is 
occasionally found upon the surface and seldom very far 
beneath it. In some the axis branches and in most the 
growing tip is advanced some distance each season, just 
as the crown of the tree-fern is lifted higher in air. The 
conditions under which our species exist, especially in 
winter, are not favourable to the formation of aerial trunks 
and they have therefore been modified for a life under 
ground. 
Ferns bear no flowers,—although one species is by 
courtesy called the flowering fern—and “ fern-seed”’ is 
still as elusive and uncertain a thing as it was in the time 
of the Ancients. Many absurd ideas were entertained 
regarding it, some of which are mentioned in the chap- 
