360 FERN FAMILY. 



§ 2. Stems annual, not living through the winter, branched, at least the sterile ones. 



!B. limbsum. Muddy edges of streams, rather common : stems all alike, 

 2° -3° high, with many furrows, fruiting in summer, and afterwards sending 

 out a few upright branches ; sheaths with 15-20 dark-colored acute teeth. 



E. arv6nse, Common Horse-tail. Moist sandy places, common N. : 

 fertile stems unbranched, with very conspicuous sheaths, 4' - 8' high, appearing 

 in earliest spring and soon withering; sterile stems 8' -20' high, producing 

 many whorls of rather rigid slender and mostly simple 4-angled branches. 



E. sylv^ticum, Woodland H. Common N., along the edges of moist 

 woods : fertile stems appearing in early spring, but lasting all summer, both 

 these and the sterile ones producing many whorls of spreading or gracefully 

 decurved compound softish 3 - 5-furrowed branches and branchlets ; sheaths of 

 the main stem loose, 8- 14-toothed. 



132. PILICES, FERN FAMILY. 



Flojverless plants with creeping or ascending rootstocks, or even 

 erect trunks, bearing distinct leaves (fronds), which are rolled up 

 (circinate) in the bud (except in one group), and bear commonly on 

 the under surface or on the edges the simple fructification, consist- 

 ing of 1 -celled spore-cases (technically called sporangia) variously 

 grouped in dots, lines, or masses, and containing but one kind of 

 minute, 1 -celled, powdery, numerous spores. A large family, most 

 abundant in warm and moist regions, consisting of 8 suborders, 6 of 

 which are represented with us. 



[The divisiotts of a pinnatijid frond are properly called segments; of a pinnate 

 frond, pinna;; of a 2-S-A-]iinntite frond, pinnid'S or ultimate segments. The stalk 

 of the frond is a stipe; its conlinuutiim tluough the frond, the rhachis ; its branches, 

 partial or secondary rhachises. A rharhls bordered by the I tafy portion becomes a 

 midrib, which may be primary, secondary, Spc] 



I. POLYPODIACEJE, or TRUE FERNS : characterized by 

 stalked spore-cases, having a vertical, incomplete, many-jointed, 

 elastic ring, which straightens at matuiity, breaking open the spore- 

 case transversely, and so discharging the spores. Spore-cases rarely 

 if ever on very narrow thread-like branches ; the fruit-dots often 

 covered by a scale-like involucre (the indusium). 



§ 1. No defnite fruit-dots, but the spore-cnses in large patches on the under surface 

 of the fertile frond, or entirely covering the under surface: no indusium. 



1. ACROSTICHUM § CHRYSODIUM. Fronds simple or pinnately branched, 



with reticulated veins : spore-cases covering the whole under surface of the 

 frond or of its upper divisions. 



2. PLATYCERIUM. Fronds irregularly forking; veins reticulated: spore-cases 



in large patches on special portions "of the under surfoce. 



§ 2. Spore-cnses on the back of the frond, sometimes near the margin, in dots or lines 

 (sori) placed on the veins or at the ends of the veins, but ivilhout indusium of 

 any kind. 



3. POLYl'ODIUM. Fronds simple or pinnate, rarely twice pinnate; veins free 



or reticulated; fruit-dots round or roundish, at the ends of the veins, or at the 

 point where several veins meet (anastomose). Stalk articulated to the root- 

 stock, and leaving a distinct scar when decayed away. 

 14. PHEGOPTERIS. Agrees with Polypodium in most respects ; but has the fruit- 

 dots smaller, and conimoiily on the veins, not at their ends, and the stalk is 

 not articulated to the rhachis. 



4. GYMNOGRAMME § CEROi'TERTS. Fronds compound, covered beneath 



with white or yellow waxy powder: fruit-dots in long often forking lin08 

 on the veins. 



