474 
Willis. — Plant Invasions of New Zealand . 
This, however, is not my own opinion ; what I maintain is that in about 
90 per cent, or perhaps more of the cases, the distribution has been by land, 
and has been chiefly mechanical, so far as its broad outline is concerned. 
Age and area must not be applied to individual cases. 
Another point whose misunderstanding is frequently a stumbling-block 
in the way of acceptance of age and area, is a confusion of the two types of 
distribution known as taxonomic and ecological. The former, with which 
alone age and area is concerned, takes no account of the density or rarity of 
a given species upon the ground, but simply of the total area over which it 
is found, while the latter is much more concerned with the density or rarity 
of a given species under a given set of ecological conditions. From the 
taxonomic or age and area point of view there is no difference between the 
species represented by the two groupings of letters below : 
00 co 
o o 
00 o o 00 
0000000000 
OOO cooooooooo 
000000000000 
00 o 0000000000 
o o 
O O OOO o 
00 00 
and in this connexion it is a pleasure to acknowledge the justice and value 
of Mrs. Arber’s criticism ( 1 ), while drawing attention to the fact that she 
incidentally refers to, that people have in general regarded species with small 
areas as species that are dying out (cf. 10, p. 349). If this can no longer be 
accepted, then my general contention that endemics of small area are not 
necessarily relics of past floras, but are usually young species that have not 
had time to spread, receives very strong support. 
Examining these zonation figures in detail, one at once finds that 
a great many genera show their maximum at the far north of New Zealand, 
like Pittosporum , Metrosideros , and Utricular ia in Table I. They do not 
show any falling off to the northwards, even though the figures may be the 
same for the first two, three, or even four zones. Now a consideration of 
Diagram I, given on p. 472, will show that the maximum of endemics must 
in general occur somewhere near to the point or zone of original entry of the 
first species to arrive from abroad. Consequently when one deals, as is now 
the case, with a large number of different genera, it is clear that the 
variations to one side or the other will cancel one another, and, therefore, 
that the region of entry into New Zealand (as now limited by the ocean) was 
within the first 300 or at most 400 miles of the northern part of the North 
