608 Transactions. 
T. venosum is flexible as well as slender, so that their fronds are pendulous 
and irregularly elongated. In this respect these two species are more 
modified than the others of this class. Occasionally, however, erect fronds 
of T. venosum may be found which are less modified from the deltoid form 
orm. Most of these small species are probably best inter- 
preted as reduction forms. The frond of H. rufescens is typically deltoid, 
and it is to be noted that H. flabellatum, to which the other species is 
undoubtedly closely allied, also frequently adopts a very similar form in 
mountain stations. 
The hairy covering of the fronds of Н. rufescens and T. Lyallii probably 
acts as a protection against drying in the same way as has been suggested 
for H. ferrugineum, and thus plays a part in enabling these species to 
endure a somewhat more exposed position than such other mountain species 
as T. Colensoi. No doubt the base of large trees at the misty altitudes at 
which these two species abound is for the most part a sheltered and humid 
station ; but the reason why they prefer high to low altitudes is best sought 
in the supposition that they are mountain forms of lowland plants. 
In the case of all these small delicate species the mat is the natural 
low epiphytes of this class are so restricted in their vertical distribution. 
(L) The High Epiphytic Stunted and Imbricated Mat Growth-form.— 
The last growth-form to be considered is that illustrated by certain normaly 
large-fronded species, which, on account of their ability to adopt the mat 
habit together with an extremely stunted and imbricated form of frond, 
These are H. sanguinolentum, H. multifidum, H. villosum, H. rarum, and 
H. flabellatum. These species all occur commonly along with the små 
H. villosum and H. multifidum are able to endure greater degrees of 
desiccation than the other species, as is shown by the fact that they alone 
gh ep : 
the lowlands these two species and H. sanguinolentum show the stunting 
of the frond and imbrication of the pinnae with inrolling of the segments, 
