APOGAMOUS FERNS. THE GENERAL PHENOMENON 



supplemented this by several important samples of material of wild and botanic garden 

 origin, the normal strain of commerce was in the first instance my principal source of 

 information. Other species, notably Pteris cretica, at a later stage showed themselves to 

 be more amenable to cytological treatment and gave better preparations more easily; 

 yet others, e.g. Dryopteris Borreri and Phegopteris, were detected as relatively abundant 

 sources of material in the British flora. All these advantages have been utilized in the 

 evolutionary analyses, but the chief historical interest still lies with Cyrtomium. Besides 



Fig. 163. Part of a frond oi Cyrtomium falcatum (L.f.) Presl from a pressed 

 greenhouse plant of commercial origin. Natural size. 



being one of the first three apogamous ferns to be discovered (de Bary, 1878), the other 

 two being Pteris cretica and Dryopteris Filix-mas (or D. Borreri) var. cristata Hort., the 

 existence of Miss Allen's rather imperfect description of the cytology quoted above 

 makes it seem of greater scientific value to emend this rather than to utilize some 

 other species, such as Pteris cretica, about which no confusion is likely to arise. 

 Before starting the description, however, it may be well to anticipate what will 

 be said in the next chapter to the extent of explaining the change of nomenclature 

 (Christensen, 1930) which has been introduced since Miss Allen's time. The old species 

 ' Aspidium falcatum', besides being relegated to a separate small genus Cyrtomium 

 composed of about a dozen species, has itself been split into three, each with a diflferent 

 geograpliical area in eastern Asia and Africa. Miss Allen's material was from Wisconsin 

 Botanic Garden and was probably C. falcatum proper, since this is the most commonly 



MFC 



161 



II 



