THE BLADDER FERNS. 211 



ovate, acute and pinnate, the pinnae rather distant, 

 broadest at base and themselves pinnatifid or again pin- 

 nate. The pinnules are narrow, bluntish, lobed or 

 toothed and usually decurrent on the rachis. There is, 

 however, a wide range in the shape and cutting of the 

 fronds. Our illustrations show two interesting forms of 

 American specimens. A pinnule is also shown in the 

 Key to the Genera. 



Not only is this species the first to put forth its fronds, 

 but it is one of the earliest to fruit and, unlike other 

 species which fruit early, fertile fronds may be found all 

 summer. Nearly every frond bears sporangia. The sori 

 are rather small and thickly scattered on the lobes of the 

 pinnules. Owing to the early withering of the indusia, 

 they usually appear as if naked. Only in the young- 

 est sori can the indusium be seen to advantage. It is 

 ovate, very thin, and taper pointed. From the shape of 

 the arching indusium, this species was anciently known 

 as the cup fern. 



The fronds of this species are very easily confused with 

 those of Woodsia obtusa, with which it often grows, and 

 the difficulty in separating them is increased by the 

 evanescent nature of the indusia in both species. In 

 Cystopteris, however, a careful search will usually reveal 

 enough shrivelled vestiges of the indusia to make identi- 

 fication sure. In Woodsia, too, the pinnae and pinnules 

 are ordinarily broader and blunter. 



In America, the common bladder fern is found from 

 British America to Georgia and Arizona. It is frequently 

 called the brittle bladder fern, a translation of its specific 

 name. The name of white-oak fern has also been given 

 it, though for what reason does not appear. Several 

 varieties have been named but none of them are very 



