FERN FAMILY. 487 



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

 consisting of 1-celled spore cases (technically called sporangia) 

 variously grouped in dots, lines, or masses (called sori or fruit 

 dots) and containing but one kind of minute, 1-celled, powdery, 

 numerous spores, which are discharged when the sporangia 

 finally split open. A large family, most abundant in warm 

 and moist regions. 



[ The divisions of a pinnatifid frond are properly called segments ; of 

 a pinnate frond, pinnm ; of a 2-3-i-pinnate frond, pinnules or ultimate 

 sefjments. The stalk of the frond is a stipe; its continuation throurjh the 

 frond, the rhachis ; its branches, partial or secondary rhachises. A rha- 

 chis bordered by the leafy .portion becomes a midrib, which may be primary , 

 secondary, e<c.] 



I. POL YPODIUM SUBFAMILY. Characterized by stalked 

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

 ring, which straightens at maturity, 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 definite fruit dots, but the spore cases in large patches on the under surface of 

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



1. ACROSTICHUM § CIIRYSODIUM. Fronds simple or pinnately branched, with retic- 



ulated 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 surface. 

 § 2. Spore cases 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 without indusium of 

 any kind. 



3. POLYPODirM. Fronds simple or pinnate, rarely tsvice pinnate; veins free or retic- 



ulated ; fruit dots round or roundish, at the ends of the veins, or at the point where 

 several veins meet (anastomose). Stalk articulated to the rootstock, and leaving a 

 distinct scar when decayed away. 

 (15. PHEGOPTERIS may be sought here.) 



4. GYMNOGRAMME § CEROPTERIS. Fronds compound, more or less covered beneath 



with white or yellow waxy powder ; Iruit dots in long often forking lines on the 

 veins. 

 6. N0THOL.^NA. Fronds once or twice pinnate, woolly, scaly or powdery beneath; 



fruit dots at the ends of the veins, formin;^ a line next the margin of the divisions. 

 § 3. Spore cases on the hack along the margin of the. frond, provided with an involucre 

 formed of its reflexed and more or less altered margin. 



6. ADIANTUM. Fruit dots at the ends of the veins, borne on the inner side of a reflexed 



portion of the margin. Stalk dark and polished, sometimes chaffy-bristly. Pinnules 

 always separate, distinctly stalked or almost sessile, but never decurrent on the 

 rhachis. 



7. PTERTS. Spore cases on a transverse, vein-like receptacle within the margin, which 



connects the ends of the veins, and is covered by the reflexed thin margin. Stalk 

 light-colored (except in § Doryopteris). Pinnules or ultimate segments adnate to 

 the rhachis, often decurrent. 



