298 FILICALES [gH. 



Dipteridinae. (Dipteris.) 



The genus Dipteris, formerly included in the Polypodiaceae, 

 has been assigned to a separate family partly on account of the 

 slight obliquity of the vertical annulus (fig. 231, G) and on other 

 grounds^. The four species Dipteris conjugata, D. Wallichii, 

 D. Lobbiana {= D. bifurcata), and D. quinquefurcata (fig. 231) 

 are characterised by a creeping rhizome bearing fronds reaching 

 a length of 50 cm. ; in D. conjugata and D. Wallichii the lamina 

 is divided by a median sinus into two symmetrical halves, while 

 in other species the leaf is dissected into narrow linear segments. 

 The main dichotomously branched ribs are connected by lateral 

 branches and these by tertiary veins, the delicate branches of 

 which end freely within the square or polygonal areolae (fig. 

 231, A', E). The naked sori are composed of numerous sporangia 

 and filamentous hairs : while in some species the soral develop- 

 ment conforms to that characteristic of the Mixtae, it has been 

 shown that in one species, D. Lobbiana (= D. bifurcata^), the 

 sporangia develope simultaneously as in the Simplices. Dipteris 

 occurs in company with Matonia on Mt Ophir and elsewhere in 

 the Malay peninsula ; it extends to the Philippines, Samoa, 

 New Caledonia, China, New Guinea, and the sub-tropical regions 

 of Northern India. 



The impossibility of drawing a hard and fast line between 

 the divisions adopted in any system of classification is well 

 illustrated by the ferns. In the main, the three-fold grouping 

 suggested by Bower is probably consistent with the order of 

 evolution of the true ferns. The Polypodiaceae, which are now 

 the dominant group, are in all probability of comparatively 

 recent origin, while the Gradatae and Simplices represent smaller 

 sub-divisions with representatives in remote geological epochs. 

 The genera Loxsoma, Matonia and Dipteris afford examples of 

 ferns exhibiting points of contact with more than one of Bower's 

 sub-divisions : they are generalised types which, like many relics 

 of the past, are now characterised by a restricted geographical 

 range. 



1 Seward and Dale (01). = Armour (07). 



