48 NEW ZEALAND PLANTS. 
the area of frequent rainy days is entered, and at once the train 
plunges into the black forest-mass, which at that point stands out 
like a wall, forbidding the tussock to advance farther west. So is 
it throughout the South Island, until the wet climate of southern 
Otago favours forest and allows it to extend from coast to coast. 
The southern-beech forest can thrive, it is true, with a smaller 
rainfall than the rain-forest, and can occupy drier ground and more 
inhospitable stations. Still, it, too, has frequently more or less a 
rain-forest character. Its chief distinction is, imdeed, floristic and 
geographical, for its leading trees belong to the southern-beech genus 
(Nothofagus), which is peculiar to New Zealand, subantarctic South 
America, Tasmania, and eastern Australia, and has no tropical 
Asiatic or Polynesian relatives. It also differs from true rain-forest 
in its tall trees being all of one kind, whereas in rain-forest there is 
a mixed assemblage, although one or two species may be in special 
abundance. Further, though there is a considerable similarity 
between the two classes of forest, and they are connected by inter- 
mediates, taxad rain-forest at one end of the series contrasts 
markedly with subalpine southern-beech forest at the other end, so 
greatly do the two differ in their composition, physiognomy, life- 
history, and biological characteristics. 
All the New Zealand rain-forest associations have a number of 
characters in common. With one or two exceptions, the trees are 
evergreen. Sometimes the bases of the trunks develop buttresses 
(fig. 29), which may be plank-like, and their uppermost roots fre- 
quently stretch over the forest-floor, half-buried, or at times raised 
high above the ground. Such roots and irregular bases of the trees 
in general are closely covered with mosses, liverworts, or perhaps 
filmy ferns. In their interstices humus lodges, in which many ferns 
and seedling plants find a fittmg home. 
The forest is made up of different layers, if the general level of 
the foliage be considered. The tall trees form the uppermost layer ; 
the smaller trees and tallest shrubs the second, or between this layer 
and the first may come the crowns of the medium-sized trees ; smaller 
shrubs, tree-ferns, sedge-tussocks, and juvenile trees the third; and 
finally comes the forest-floor, with its carpet of mosses, liverworts, 
and filmy ferns, through which grow the smaller ferns (fig. 33), herbs, 
grass-like plants, and seedling trees and shrubs. A most important 
feature of the forests is afforded by the climbing-plants, or lanes. 
