258 THE SENSITIVE AND OSTRICH FERNS. 
in shape, and upon examination prove to be much like 
the sterile pinne, except that each edge is tightly rolled 
over to the midrib, forming two parallel chambers in 
which the sori are enclosed. Cut across the end, a pinna 
reminds one of two tiny gun-barrels and the likeness 
is heightened by the black, powdery spores that sift out. 
The books are either silent inregard to the indusium, 
or assert that this species has none, but according to 
Eaton there is a scale-like indusium at the base of each 
sorus. This is only to be seen in very young fronds 
and resembles that of Oxoclea. Fronds intermediate be- 
tween fertile and sterile are occasionally found, and 
may be produced artificially by cutting off the sterile 
fronds early in the year. The sterile fronds die in au- 
tumn but the fertile, like those of the sensitive fern, 
survive the winter, although to all appearances dead. 
The spores are not released until spring, when they 
readily germinate. Since they contain chlorophyll they 
are not able to retain their vitality for much longer than 
a year. 
When the ostrich fern gains a foothold in a locality, it 
spreads rapidly by means of stolons. These are de- 
veloped from adventitious buds on the rootstock at the 
bases of the old fronds. Large numbers of them remain 
dormant but a few usually develop into slender runners 
that wander about in the earth and finally throw up a 
new crown of fronds from the tip at some distance from 
the parent plant. 
The common name is due to an imagined likeness of 
the fronds to an ostrich feather. It is sometimes known 
as ostrich-feather fern. In Europe it has been called 
two-ranked fern because its fertile fronds have two rows 
of fruiting pinnules. The name of shuttlecock fern is 
