2\ Willis . — The Flora of Stewart Island [New Zealand) : 
mere fact that one can make so many predictions about any of the floras of 
the New Zealand region, and find, on verification of the facts, that they are 
justified, is alone sufficient to show this. The principal cause that interferes 
with the uniformity of the action of age and area is the presence of actual' 
barriers, such as Cook’s Strait, Foveaux Strait, the central mountain chain, 
the sea dividing New Zealand from the outlying islands, and so on, but 
within New Zealand the actual ecological barriers, which might easily alter 
very largely the distribution of species if they were of sufficient breadth and 
width, do not seem to affect the question of area occupied, save in quite 
a minor degree. The plants are locally distributed, within the area which 
is assigned to them by the passage of time, in accordance with their 
reactions to the various ecological factors which are operative there. But 
ecology seems little concerned, so far as we can see, and so far as the 
figures of distribution give any guide, with the actual composition of the 
flora. Unfavourable ecological conditions may determine that a certain 
species shall not survive in a given place, so that it may reach what, in 
a list of modifying causes we have given in a previous paper (6, p. 206), we 
have termed the climatic boundary, but which might better perhaps be 
termed in a more general way the ecological boundary. But otherwise 
ecology simply seems to make what it can, so to speak, of the floras 
with which it is provided by the mere action of phylogenetic descent and 
of time. 
That the composition of the flora of Stewart is what it is, is largely due 
to the simple fact that certain species were at a certain distance from 
Stewart early enough to arrive there before the formation of Foveaux 
Strait, which cut it off from New Zealand proper. The figures of distribu- 
tion give little evidence to show that many species have arrived since the 
formation of the strait, though there are a few, for example Ur tic a australis ^ 
which seem to be such cases. In general the distribution follows age and 
area with such closeness that one may make predictions on this basis alone, 
and find them often within perhaps five per cent, of accuracy. 
It is worth while pointing out that by using the hypothesis of age and 
area one finds great numbers of new facts ready to be picked up, or explana- 
tions of what have hitherto been regarded as facts to be simply accepted 
as such. As one has as yet no guide as to their relative immediate impor- 
tance, one must be content to collect them all, and no doubt they will in 
time prove their comparative values. 
Stewart Island is a small island of 664 square miles, separated from 
South Island by Foveaux Strait, which at its narrowest has a breadth of 
sixteen miles, and at its shallowest (centre) a depth of fifteen fathoms (thirty 
metres). It would therefore seem not unreasonable to suppose that the 
separation from South Island was at a very remote period. This is con- 
firmed by the fact that Stewart possesses local endemic species, confined 
