THE UNCOILING FRONDS. 19 
we have ultimate pinnules or ultimate segments for the 
smallest divisions, though pinnule is often loosely-used 
to designate them all. 
Another peculiarity of fern fronds is the way in which 
they are veined. Instead of giving off branches at inter- 
vals, as in flowering plants the veins, fork near the base 
and each fork may fork and fork again. ‘Thus one vein 
is usually equal to any other in the frond. Commonly 
the veins do not connect with one another, when they are 
said to be free. If connecting they are said to be anasto- 
mose and the meshes of the net-work thus formed are 
termed areole. 
Ferns are separated into families upon characters taken 
chiefly from the rootstock, the manner of veining, and 
the shape and position of the sori and indusia. The 
indusium is a remarkably unvarying feature, and of itself 
forms a kind of family escutcheon from which the genus 
can usually be determined at a glance. Thus the indusia 
in the Polystechums are circular; in the Woodsias, star- 
shaped; and in the Asfleniums, linear. The distinguish- 
ing characteristics of the other genera may be found by 
referring to the “key” at the back of the book. 
