24 
THE FERN WORLD 
or urn in which the spore cases are contained, and which in 
the same way at the proper season liberates the latter by 
bursting. 
Some Ferns possess two kinds of fronds, barren and fruit- 
ful, the former bearing spores, and the latter being without 
them. In some instances the two kinds of fronds are not 
distinguishable from each other. But in other instances the 
form of the fruitful frond materially differs from the barren 
one. The relative lengths of the stipes and of the leafy 
portion in fronds vary considerably in different species. 
Sometimes they are equal, sometimes the stipes is much 
longer than the leafy part of the frond, and sometimes the 
contrary is the case. 
