THE OAK FERN 



21 



ical importance, but very helpful in distinguishing it 

 from its near ally, the Lime stone-Polypody) is its per- 

 fect smoothness, a constant distinction, most easily seen 

 on the stipes and rachis, but equally occurring over the 

 whole plant. The fronds are divided so that each 

 branch is pinnate at the base, pinnatifid toward the 

 point ; the pinnae are also pinnate at their bases, then 

 pinnatifid, and at their points acute and nearly entire ; 

 the pinnules and ultimate lobes are oblong and obtuse, 

 with a rather wavy midvein, from which the venules 

 branch alternately, extending to the margin, in those 

 of moderate size simple with a sorus at each extremity, 

 in the larger branched with the sorus on the lower 

 branch. The fructification varies much, according to 

 habitat and season, being sometimes very much crowded 

 and sometimes very 

 sparse. The spore- 

 cases are small, round- 

 ish obovate (inversely 

 egg-shaped), and at- 

 tached by a slender 

 stalk ; the spores 

 ovate (egg-shaped), 

 oblong, or roundish, 

 with a granular sur- 

 face. 



Like the Beech 

 Fern, the Dryopteris 

 is found from the 

 coast-level to a great 

 elevation. It is seen 



c 3 



