HOW TO IDENTIFY THE SHIELD FERNS. 



EVEN the beginner in the study of ferns finds it fairly easy to 

 distinguish between the members of the smaller genera, 

 like Osmunda and Woodwardia, but with genera such as 

 Asplenium and Dryopteris, there are so many species that he is 

 quite likely to become confused and wonder if it is possible to 

 name them correctly at all. In Northeastern America, the genus 

 Asplenium presents the fewer difficulties, for the species have no 

 very striking superficial resemblances, but in Dryopteris the 

 family likeness is stamped so distinctly upon all, that a few hints 

 regarding their identification may not come amiss. 



For the purposes of our study, the genus Dryopteris may be 

 said to contain those ferns which bear upon the under side of the 

 fronds round fruit dots covered with an indusium which is fixed 

 to the frond by its depressed centre or by a sinus at one side. 

 This difference in the way the indusium is fastened to the frond 

 serves admirably to divide our species into two groups. The 

 first, containing those species having an indusium fixed by the 

 depressed centre has been placed in a separate genus {Polysti- 

 chum) by English students, a proceeding which might well be 

 followed in this country. 



Taking our Polystichums, then, it is found that we have 

 three species. The first is the well known Christmas fern {D. 

 acrostichoides), common throughout the Northeastern States. It 

 is evergreen, simply pinnate, and the upper part of the frond, 

 which bears the fruit, is abruptly contracted. No other species is 

 thus contracted at the summit. 



The Holly fern (D. lonchitis) is plentiful in parts of British 

 America, but does not stray into the United States in the east. 

 Like the preceding, it is simply pinnate, but the fruiting portion 

 is not contracted. This point distinguishes it. 



The third species, Dryopteris Braunii, is a tall stately fern 

 with at least twice-pinnate fronds, found in the deep cool shades 

 of New York, New England and northward. It is the only east- 

 ern species with more than once-pinnate fronds, whose indusia 

 are fixed by the depressed centre, and it may further be distin- 

 guished by its very chaffy rachis. 



This brings us back to what we are pleased to consider the 

 true Dryopterids. Of these, there is one species fairly common 

 in damp rich woods throughout the Northeastern States, in which 

 the pinnae as we proceed toward the rootstock are gradually 



