LASTR.EA THELYPTEK1S. 185 
/* LASTRJS'A THELYTTERIS. 
THIS has been called by different botanists Acrostichum, 
Aspidium, Athyrium, Hemestlieum, Polypodium, and 
Polystichum ; but they all agree iu giving it the specific 
name of Thelypteris, which is literally the Woman or 
Lady Fern. In English it is known as the Marsh 
Shield Fern, Marsh Polypody, and Marsh Fern. 
Root widely creeping, by means of slender, blackish, 
thread-shaped, smooth, or slightly downy ruuners. 
From various points in these arise irregularly the/rontfr. 
These are erect, delicate, deep green, usually smooth, 
but occasionally slightly hairy. The barren fronds aro 
about one foot high, but the fertile fronds vary from two 
to four feet in height. Their stem is slender, and 
mostly naked, but sometimes slightly scaly, and the 
lower half without leaflets. These, especially when 
ban-en, grow markedly horizontally, are narrow spear- 
head shaped, deeply and regularly pinuatifid, partially 
opposite, but mostly alternate ; the barren segments 
blunt, and slightly scolloped; the fertile segments 
narrower, more pointed, with the edges rolled back. 
The mid-vein zigzagged, and sometimes very hairy. 
The lateral veins divide into two branches about half- 
way between the mid-vein and margin of the segment, 
and on the fertile fronds each branch of the lateral 
veins bears a small round mass of the fructification. 
Each mass is dark brown, at first covered by a thin, 
white, torn, kidney-shaped cover (indusium), fixed by the 
