104 



CONIOPTEEIS. 



C. hymenophylloides. Lindley & Hutton instituted two species, 

 Tympanophora simplex and T. racemosa ; Bunbury described another 

 species in which the lamina of the fertile pinnules is less reduced, 

 as in Sphenopteris nephrocarpa, and compared this type with recent 

 species of Bichonia. All these can, however, be connected by 

 intermediate forms, and we have insufficient evidence to justify 

 their recognition as distinct species. In the Tympanoplwra simplex 



Fig. 13. — Dicksonia Bcrtervana, Hook. (From a specimen in the 

 British Museum Herharium.) 



type the sori are larger and more prominent than in T. racemosa, 

 of which a single pinnule bears several sori ; this difference is, 

 however, most probably due to a form of compensation, that is 

 to say, where we have one sorus on a pinnule the production of 

 sporangia is greater than in cases where the sporiferous tissue 

 is less concentrated and divided between four or five sori. 

 Moreover, in such a specimen as that in Fig. 3, PI. XXI. we 



