CHAPTER XLV 



DIPTEROID FERNS 



Though Matonia and Dipteris have long been recognised as probable 

 survivals from an earlier age, they were till recent years regarded as isolated 

 and perhaps derelict types. Little attempt had been made to connect them 

 with Ferns of the present day. Hitherto this may appear true for Matonia: 

 its nearest relatives are probably found amongst the Dipteroids and Gleicheni- 

 aceae. But discoveries among the Mesozoic fossils, together with a better 

 knowledge of certain other living Ferns which share in more or less degree 

 with Dipteris its general features, have combined to show with high probability 

 that the Dipteroid type survives in a considerable section of the modern 

 Leptosporangiate Ferns. In particular it is rapidly becoming clear that many 

 of those ranked in the comprehensive but phyletically confused genus 

 '' Polypodiniii' are really Dipteroid derivatives, which never in the course 

 of their descent were gradate, nor possessed an indusium protecting their 

 naked superficial sori. 



The first step in building up such conclusions will be to search for the 

 nearest connecting forms, and to work upwards from them. An aid to their 

 recognition is the existence of a rich synonymy, applied it may be to some 

 type peculiar in form, and difficult of classification. Such a type is found in 

 Cheiropleuria biciispis (Bl.) Presl, which after vicissitudes of terminology is 

 now recognised as the sole representative of a substantive genus Cheiropleuria 

 Presl, 1849 (see Studies V, AuJi. of Bat. XXIX (191 5), p. 495). 



Cheiropleuria bicuspis (Bl.) Presl 



This Fern is widelydistributed in the Malayan region, where it iscommonly 

 associated with Dipteris conjugata, a fact that is probably more than a mere 

 coincidence. It was figured by Hooker {Loud. Journ. Bot. Vol. V, p. 193, 

 Pis. 7, 8), and his drawing has been widely quoted. The sterile leaf there 

 depicted is bicusped, but comparison of specimens shows that it is variable 

 in its outline, as will be gathered from the photographs shown in Fig. 709, 

 a-d. Not uncommonly the sterile blade is quite unbranched. 



The axis is elongated, with internodes of varying length. It is densely 

 clothed with silky yellow hairs, and bears many brown roots. The plant 

 hovers between a terrestrial and an epiphytic habit ; as Van Rosenburgh 

 says, it is "creeping or subscandent" (^Malayan Ferns, p. 732, 1909). Dicho- 

 tomous branching of the axis has not been observed, but lateral buds are 

 frequent, arising from the abaxial face at the base of many leaves, though not 



