222 THE CHAIN FERNS. 
only to the sterile fronds. Since both the sensitive fern 
and the chain fern fruit late in the year, there is a large 
part of the season when they are easily confused, espe- 
cially if the collector has never seen both growing. It is 
not to be inferred, however, that it is impossible, or even 
difficult, to separate the species when sterile. When 
they are in fruit there is, of course, no chance of mis- 
taking them. 
The rootstock is quite slender and creeping and the 
fronds somewhat scattered along it. The sterile are 
twelve to twenty inches long with slender, straw-coloured 
stipes and ovate blades cut nearly to the midrib into 
oblong, acute lobes. Toward the base, the lobes incline 
to be separate, the part nearest the rachis being rapidly 
narrowed into a broadly winged stalk. This makes the 
blade appear pinnate, at least at base, but there is usually 
a narrow wing of membrane connecting even the lowest 
division with the rest. All the pinnules are finely ser- 
rate on the edges. 
In June the taller fertile fronds begin to come up. 
They are on longer stipes and quite unlike the sterile 
fronds. Even the stipe is of a different colour, being 
black and polished, while the blade is distinctly pinnate 
with long, narrowly-linear, distant pinnules that seem 
just wide enough to hold the two lines of large, heavy, 
sunken sori. None of our other ferns have an indusium 
so thick and corky, and perhaps for this reason the fer- 
tile fronds are much heavier than the sterile. Long 
after its usefulness has departed, this indusium remains 
attached to the frond. There are many curious grada- 
tions between fertile and sterile fronds both in the shape 
of the pinnules and in fruitfulness. In the northern 
part of its range, at least, this species is not evergreen 
