NEW ZEALAND FERNS 53 



species form, at times, short trunks, those of L. superba being the 

 larger, more or less conical in shape, and sometimes measuring 

 44 cm. in diameter at the base and 50 cm. in height. The colour 

 of the fronds bears a relation to the intensity of the illumination, 

 the leaves being blackish green in the most feeble light. So too 

 does Blechnum nigrum, a fern of the moistest and darkest forest 

 gullies, possess almost black fronds. 11 



The ferns noted up to the present have shown striking ephar- 

 mony, but the examples next to be cited clearly show that mis- 

 leading conclusions may be drawn from structure which appar- 

 ently could possibly fit in with only one set of conditions. 



Rangitoto Island, a volcanic cone rising out of the Hauraki 

 Gulf at the entrance to Auckland Harbour, offers for plant coloni- 

 zation merely irregular blocks of lava, large and small. At the 

 present time, although there are many bare patches, there is a 

 surprising amount of vegetation, varying from isolated plants just 

 gaining a footing to actual low forest which has formed a true 

 soil. Leaving certain mosses and lichens out of consideration, 

 the plants consist in large part of trees and shrubs which, if not 

 xerophytes, have epharmonically assumed xerophytic adaptations. 

 There are also certain herbs and ferns. Amongst the latter two 

 filmy ferns grow right on the dry bare rock exposed to the full 

 rays of the sun. These are Hymenophyllum sanguinolentum and 

 Trichomanes reniforme, the former usually an epiphyte of forest 

 or even open scrub, and so naturally attuned to a certain amount 

 of drought, but the latter elsewhere to be found only in the wettest 

 forests, where usually all is dripping with moisture. Its presence, 

 but for the fact of this Rangitoto habitat, might well be taken as a 

 certain sign of superabundant rainy days. It is true that T. reni- 

 forme is not confined to the bare lava alone. It grows also where 

 there is a little soil on the rock, or rises out of a patch of liverworts. 

 Or, it may be found at the base of clumps of Astelia Cunninghamii 

 var. Hookeriana (Liliaceae), a xerophyte of the tussock form fur- 

 nished with long, linear, rigid, coriaceous leaves, but this station 



11 Trichomanes elongation, which occupies the darkest and most hygrophytic 

 station of all the New Zealand Hymenophyllaceae, has very dark-coloured fronds, 

 which are frequently covered with many epiphytic mosses and liverworts. 



