322 DIPTERIDACEAE [CH. 



The features of specialised advance, recognised partly on comparative 

 grounds, and not always demonstrated in strict stratigraphical sequence, 

 have been: (i) the development of helicoid dichopodial branching of the 

 lamina; (ii) webbing of the leaf-segments; (iii) fusion of veins to form the 

 venatio anaxeti; (iv) advance to solenostely with ultimate disintegration of 

 the leaf-trace; (v) spread of the sori over the enlarged leaf-surface, with a 

 tendency to lose the soral identity in an Acrostichoid state; (vi) increase in 

 number of sporangia in the individual sorus, with indications of transition 

 to the "mixed state"; (vii) diminution in size of the individual sporangium, 

 with reduction of the spore-output of each from such a figure as 512 to 64. 

 All of these are indications of advance as regarded from the point of view 



Fig. 580. Photograph by Mr Tansley of Diptcris conjjigala 

 \= Horsjieldii) on the edge of Padang Batu, Mt Ophir, 

 showing its native habit (much reduced). 



detailed in Vol. I, and the palaeontological evidence tends, so far as it goes, 

 to support the general progression in time from the Rhaetic period onwards 

 to the present. It is specially significant that, while certain archaic features 

 still survive in the living species of Dipteris, none of them show either a 

 radiate uniseriate sorus with {q\n sporangia, as Matonia does, nor a spore- 

 output higher than 64 from each. But it remains to be seen how far this 

 result is borne out by the living Ferns that comparison indicates as further 

 derivatives from the Dipterid-stock ; and in particular Cheiropleuria. 



The occurrence of Matonia and Dipteris as living Ferns in the Malayan 

 region, and particularly their survival together on the heights of Mount 

 Ophir, has long been a fact of commanding interest (Fig. 580). But palaeo- 

 geography shows that in Mesozoic times the spread of the Matonia- Dipter-is 



