212 BOTANY 
storms. When mist and rain are absent and the sun 
shines through the rarefied atmosphere, the heat 
is often intense and transpiration therefore extremely 
active. At night again this rarefied condition 
of the air permits of rapid radiation to the clear 
sky, and, even in summer, frosts are of frequent 
oceurrence. As adaptations to these harsh conditions, 
numerous peculiarities of habit and structure have 
appeared in plants that form these alpine meadows. 
Tio guard against injury by storm, and, at the same 
time, by imprisoning the air to reduce extremes of 
heat and cold, the cushion and rosette habits, the former 
well seen in the mountain rimu and New Zealand 
donatia, and the latter in the great variety of celmisias, 
have been assumed. To check transpiration, which, 
owing to constant wind and intense heat, would at 
times, be excessive, special adaptations of leaf surface, 
structure and position have arisen. In the spear-grasses 
the leaf is hard and leathery with an extremely thick 
cuticle, and at the same time is placed in an almost 
vertical position, so that it is only in the early morning 
and late evening that it can receive on its blades the 
direct rays of the sun. The most frequent adaptation, 
however, is the dense mat of hairs that covers the 
under-sides of the leaves, as seen in the celmisias and 
many other plants of this family. These hairs, as we 
have already noted, not only check the eseape of tran- 
spired vapour, but, at the same time, by forming a 
non-conducting layer, modify extremes of heat and 
eold. 
SUCCESSIONS. 
Tt often happens that, in a particular locality, one 
plant society succeeds another. Indeed, if we consider 
for a moment we shall see that the vegetation of the 
earth as it stands to-day must be the product of a 
long series of such successions. Much can be learned 
