FRUCTIFICATION IN FERNS. 1$ 



vein, covered by a continuous and distinctly intramarginal indu- 

 sium. This genus closely resembles the 

 next in general habit, and is sometimes 

 united with it. 



42. Blechnum. — In this genus the 

 sori are linear and near the midvein, and 

 are covered by a membranous indusium 

 which is fixed at its outer margin, burst- 

 ing at its inner margin when the spo- 

 rangia are mature. A single representa- _ ^ , ■ • ■ 



. . ,.,. ° ^ Fig. t.— Strut k lofiterts spt- 



tive IS found Withm our limits. cant. Enlarged section of 



^^ ,,, . .. «,, . the contracted fertile pinna, 



43. Woodwardia. — Three species showing intramarginal indu- 



of chain-ferns occur within our limits, ^""°" 

 and each represents a distinct section based on the methods 

 of venation. All have oblong or linear sori more or less 

 sunken in the frond, covered by special lid-lilie indusia burst- 

 ing at their inner margins, and arranged in chainlike rows near 

 the midvein, thus giving the popular name to the genus. 



§ EuwoODWARDiA has uniform fronds and veins forming at 

 least one series of areolae between the sori and the margin. 



§ Anchistea has also uniform fronds, but with free veins 

 from the sori to the margin while § Lorinseria has dimor- 

 phous fronds, and the veins everywhere uniting to form areolae, 

 as in the sensitive- fern (Onoclea sensibtlis). 



44. Aspleniunn. — The numerous species of spleenworts 

 are closely related to each other in their methods of fructifica- 

 tion, but differ widely in the form, texture, and cutting of their 

 fronds. The sori are placed on the upper side of an oblique 

 vein (sometimes crossing it in § Athyrium), and covered by an 

 indusium of the same shape attached by its edge to the fruiting 

 vein and opening toward the midvein. In some species part 

 of the indusia are double. The veins are free in all our species. 

 In § EuASPLENiUM the sori are straight or slightly curved ; in 

 § Athyrium they are often curved, even horseshoe shaped ; 

 and frequently cross to the outer side of the fruiting vein. 



45. Phyllitis bears the linear sori in pairs, one from the 

 upper side of a veinlet and its mate from the lower side of the 

 next. The indusia are attached by their edges to the veins, and 

 folding toward each other appear like a double indusium cover- 



