eo RERTETTE 
Epharmonie variation and general epharmony.' 203 
or in the subalpine scrub between Gaya Lyallii with its thin drip-point leaves 
and nearly all the other scrub species. The truth seems to be that xerophily 
in New Zealand generally is out of all proportion to the habitats provided and 
that, as DIELS (1896: 247 and 296—298) suggested from a study of leaf-anatomy, 
it is to be referred to an ancient climate rather. than to that of the present 
day. At the same time, it is a fact, as is shown above, that in xerophytic or 
mesophytic habitats xerophytes or mesophytes rule and that the present con- 
ditions are quite sufficient to turn xerophytes into mesophytes and vice versa, 
but it must not be forgotten that such plasticity is most likely an hereditary 
character dating from certain ecological conditions in the geological history of 
New Zealand, or some other land from which the species has come. 
Chapter IV. The Plant Formations of the High Mountains, 
1. Subalpine Forest. 
a. General. 
The subalpine forests belong to to two distinct classes, namely those in which 
species of Nothofagus dominate and those where this genus is absent and there 
is a mixed association of the rain-forest type. 
The exact reasons for the presence of either class of forest are not known, 
" but in many cases, the dominance of Nothofagus is correlated with comparatively 
dry conditions which arise either from climate or a specially porous soil. On 
the other hand, either class of forest may flourish in an extremely wet area 
as is the case with the mixed subalpine forest of the Western and the Notho- 
fagus-forest of the Fiord botanical districts. Possibly, as suggested in Part IV, 
the present distribution of the two classes of forest depends, in part, upon 
historical causes. 
b. Nothofagus-forest. 
ı. General. 
It is hardly possible to draw a line of demarcation between the Norhofagus- 
association of the high mountains and that of the lowlands adjacent, but the 
former may be distinguished, in its typical form, by its more open character and 
specific constitution. N. cliffortioides (Plate XXXIX, Figs. 55, 56) is frequently 
dominant, the other species of the genus being absent over wide areas. 
The distribution of the three mountain species of Nothofagus depends 
upon their relative xerophily, N. clffortioides, the most xerophytic, occupying 
the driest and loftiest stations. N. Menziesii with its leaves thicker and smaller 
than those of N. fusca, and its greater epharmonic plasticity, comes midway 
in its requirements, and so, where the precipitation is excessive, it may form 
the sole subalpine forest, N. fusca dominating at a lower altitude. Where the \ 
tree species occur in the same locality, N. fusca, mixed more or less with 
