296 FILICALES [CH. 



sori hang down from the fronds in masses, looking just hke 

 masses of millet seed^" The sporangia are described by Bower^ 

 as large and of rather peculiar form. As seen in fig. 224, H, the 

 annulus is continuous; it forms a twisted loop of cells which 

 vary in shape and in the thickness of the walls. The Cyatheaceae 

 are for the most part tropical ferns with a wide geographical 

 range, usually in moist regions ; they are, however, able to 

 flourish under widely different temperature conditions. In 

 Tasmania, as Diels^ points out, tree ferns may occasionally be 

 seen laden with snow, and on the west coast of New Zealand 

 they overhang the edge of a glacier*. The monotypic genus 

 Thyrsopteris is confined to Juan Fernandez. The Cyatheaceae 

 no longer exist in Europe. 



Dennstaedtiinae. (Microlepia, Dennstaedtia .) 



This sub-tribe, instituted by Prantl, has been revived by 

 Bower on the ground that the sori present features inter- 

 mediate between those of Cyatheaceae and the Polypodia- 

 ceous genus Davallia. The sporangia have a slightly oblique 

 annulus. 



Polypodiaceae. 



This section of the Leptosporangiate ferns, including several 

 sub- tribes, comprises the great majority of recent genera. The 

 sporangia form naked or indusiate sori and have a vertical in- 

 complete annulus. In Plagiogyria^ the oblique annulus and 

 soral features suggest comparison with the Cyatheaceae. A 

 more intimate acquaintance with Polypodiaceous ferns will 

 undoubtedly demonstrate the -existence of other generalised 

 types®. 



From the point of view of the identification of fossil ferns 

 it is important to bear in mind the very close resemblance 

 presented by some Polypodiaceous species, e.g. species of 

 Davallia (fig. 229, C), to Cyatheaceous ferns (cf. fig. 229, D). 



1 Challenger Reports (85) p. 827. (Narrative, PI. ii.) 



2 Bower (00) p. 68. s Dials (02) p. 117. 

 * Seward (92) p. 45. ^ Bower (00) p. 80. 



' Prof. Bower informs me that he is now at work on Plagiogyria and other 

 Polypodiaceae. 



