INTRODUCTION TO CRYPTOGAMIC BOTANY. 541 



widely distributed. With the exception of Ceferach, the other 

 genera are tropical. The old Asjdeniuin Nidus, familiar as 

 an object of cultivation and one of the noblest of ferns, belongs 

 to the genus Neottopteris. 



616. BlechnuTYi is the typical genus of the fourth section' 

 Athyrium, which comprises our Filix fcemina, though in 

 some measure approaching the next tribe, is distinguished by 

 the decidedly linear junction of the indusium with the frond. 

 In A. latifolium, however, it is often curved so as to make the 

 indusium reniform. The straight sori are, indeed, the rarer of 

 the two. The indusium is at length reflected by the growth 

 of the sporangia. Doodia and Woodwardia are two closely 

 allied genera. In both the sori are short and parallel to the 

 costa on transverse veins. In Doodia, however, the indusium 

 is flat, and in Woodivaixlia immersed and convex. In the 

 former the veins and veinlets are raised beneath and more 

 distinct from the costa. Blechnum has the sori more or less 

 confluent, with the free side of the indusium towards the costa. 

 The Brazilian Salpichlcena is distinguished by its climbing 

 habit, and by the venules being combined by a transverse 

 slight infra-marginal vein. The indusium, moreover, is very 

 long and cylindrical, and bears part of the sporangia upon its 

 line of attachment. Blechnum is easily confounded with 

 Lomaria, in which the indusium is formed from the altered 

 margin of the frond, while in Blechnum it is perfectly distinct. 

 Actinio2:)teris (Fig. 113, a) appears to be a true ally of Asple- 

 niuTYi, though its marginal indusia appear at first to indicate 

 a different affinity.* The genera are indifferently tropical or 

 temperate. Doodia extends to New Zealand, and both that 

 genus and Woodwardia occur in the United States. Athy- 

 Tiu7)i and Blechnum are both tropical and extratropical, 

 varying much in size. 



6]?. The section of which Cystopteris is typical is some- 

 what analogous to Cyatheaceoe. The indusium of Cystopteris, 

 a well-known European genus, though not confined to the 

 northern hemisphere, is suborbicular, and fixed by a lateral 



* The origin of tlie indusium from the vein is not properly expressed 

 in the woodcut as it was in the original drawing. 



