366 Willis .— The Sources and Distribution of the 
Summary. 
The paper is a reply to criticism, and brings up new facts about the 
distribution of plants in New Zealand. It is shown that age and area now 
occupies a strong position, because by its aid numerous prophecies as to 
geographical distribution of plants have already been made, and have proved 
to be correct upon examination of the facts. 
Incidentally the flora of introductions into Ceylon is analysed, and it is 
shown that there is practically no evidence of large spread without the aid 
of man. 
To make more clear the true meaning of the tables of figures that have 
been published, diagrams are given, showing the range in New Zealand of 
the species of Ranunculus and other genera. Their resemblance to the 
rings made by throwing a stone into a pool will at once be noticed, and is 
a strong argument against any but a mechanical explanation of these ranges. 
The wides range farthest, the endemics successively less. 
A section is devoted to the activity of other factors than age, which 
have already been considered in detail in other papers. The question 
whether endemics are chiefly relicts is then discussed, and it is shown that 
for the vast majority the evidence is much against such being the case. 
Explanation by age and area is simpler and more convincing. Natural 
Selection cannot explain such cases as Ranunculus Lyallii , which are very 
numerous. Finally, there is given a list of twenty-eight awkward questions 
for the supporters of the dying-out hypothesis, questions which if not 
successfully answered are very damaging to that hypothesis. 
The relative age of herbs, shrubs, and trees is then dealt with by show¬ 
ing that this question is really very complex, and at present far beyond the 
capacity of age and area to answer. The figures already given for distribution 
in New Zealand are analysed, and it is shown that thirty-three or more families 
have their maximum at the far north, and taper down steadily to the south. 
This goes to show that there must probably have been a northern land 
bridge reaching New Zealand from some part of Inclo-Malaya (probably 
N. Australia), and similarly there are eighteen or more families which must 
probably have reached New Zealand by a southern bridge from some 
region abroad. The northern families are mainly trees and shrubs, the 
southern herbs. This alone shows how difficult is the question of relative 
age, and it is also pointed out that I have not claimed the same age for two 
plants occupying the same area, unless systematically related. Nor, it seems 
to me, are age and area and greater age of trees incompatible hypotheses. 
Dr. Sinnott’s hypothesis of swamping is considered, and it is shown 
that while it may have certain probabilities in its favour, the evidence is 
very conflicting. It is more common on the whole in genera of very ancient 
arrival in New Zealand, but it is also much more common in trees and 
