FERNS 449 



3. ASPIDIE.E. Sori covered with a circular or roundish indusium, springing 

 from the back of the veins. 



(a) If the son are dorsal, with round, target, or kidney-shaped indusia 

 Aspidium. 



(b) If son are round, with kidney-shaped indusium Nephrodium. 



4. ASPLENIE.E. Sori covered with an oblong or elongated indusium spring- 

 ing from the sides of the veins. 



(a) If the indusium is straight and elongated Asplenium. 



(b) If sori are elongated and in parallel pairs, with indusium opening along 

 the centre Scohpendrium. 



(c) If the sori are hidden amongst rusty, chaffy scales, with indusium 

 invisible Ceterach. 



5. BLECHNEJS. The sori have indusia, and form longitudinal lines between 

 the midrib and the margins of the pinnae, or leaflets. 



Sori, which are dorsal, are covered by a linear indusium Blechnum. 



6. PTERIDEJE. The sori are on the margins of the fronds, and are covered 

 by a special indusium. 



Sori in a continuous line at the edge of the frond Pteris. 



7. ADIANTE^;. Here the margins of the fronds are turned back, forming 

 indusia, which have the sori underneath. 



Sori in patches, under the reflexed indusium Adiantium. 



8. CYSTOPTERIDE.E. The sori have a special ovate indusium attached 

 behind, and bent over them like a hood Cystopteris. 



9. WOODSIE.E. The sori have a circular indusium springing from the 

 back of the veins, and attached beneath them Woodsia. 



10. HYMENOPHYLLE^;. The sori are at the end of the veins, and project 

 from the margin, being surrounded by urn-shaped and two-valved membranes. 

 When urn-shaped Trichomanes ; when two-valved HymenophyUum. 



n. OSMUND ACE^;. Sori have no ring, but burst vertically by two regular 

 valves. Fronds circinate Osmunda. 



12. OPHIOGLOSSACE^. Sori without ring, and two-valved ; young fronds 

 folded up straight. 



(a) Sori in irregularly branched clusters on a separate branch of the frond 

 Botrychium. 



(b) Sori sessile, in two-ranked simple spikes on a separate frond Ophio- 

 glossum. 



Many of our British ferns are very rare, and the majority of them are local ; 

 but the following notes on some of the commoner varieties will be of use to the 

 student : 



1. The Common Polypody (Polypodium vulgar e). Roots thick, woody, 

 creeping. Fronds 6 to 12 inches, broadly oblong, lanceolate. Fructification 

 conspicuous, generally at upper part of frond ; golden circular patches. Found 

 on old trees, roofs, walls, and rocks. Once a remedy for colds and coughs. 



2. Oak Fern (Polypodium dryopteris). Roots a dense matted mass. Stem 



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