PREFACE. 
XI 
The most remarkable example of this class is the robust 
Woodwardia radicans, a Fern of warm regions in both 
hemispheres. In the narrow ravines of South Italy, its 
fronds stretch from side to side of the volcanic tufa, rooting 
at their extremity ; and, from thence vegetating new 
fronds which ascend and root again and again, they form, 
as it were, a zigzag ladder by this repetition of the rooting 
process. 
3. The Costa undergoes the same changes in bifurcation 
as the Each is, from which, on that account, it is difficult to 
distinguish it : but it has peculiarities which deserve re- 
mark : First, it has a tendency to enlargement in substance 
and breadth, which, if not accompanied by a corresponding 
widening of the lamina or leafy part, causes the leaf to curl 
back, as may be observed in Lastrea dilatata, when growing 
in dry stony places, as well as in L. filix mas : but a second 
peculiarity noticeable in the Costa is the divarication of the 
pinnules at various angles. In Athyrium filix-foemina 
Fieldii, the pinnse diverge in many of the fronds so regularly 
as to form a succession of right-angled crosses, f. 4 and N.F., 
Fig. 4 a. 
