Species and other Controversial Points . 
207 
Summary, 
The paper is chiefly a reply to the criticisms of my Ceylon work 
by Mr. H. N. Ridley in the October Annals, but contains a few new 
facts also. Mr. Ridley’s criticisms are in reality answered in advance by 
my work on New Zealand. 
It is shown that the Ceylon results cannot be accidental nor deter- 
mined solely by the numbers of specimens in the herbarium, and that 
the figures are far too numerous to be disturbed by bringing up excep- 
tions, as Mr. Ridley does. 
Man’s action, changes of climate, and similar disturbing factors, were 
not sufficiently emphasized in my Ceylon paper, but have since been 
dealt with. 
Evidence is then given to show that the endemic species are on the 
whole the youngest, not the oldest, in a country. There may be relics 
also, but they are not numerous enough to show in the figures. This is 
supported by two crucial cases : one showing that the wides of New Zea- 
land take no notice of Cook’s Strait in their distribution, while the 
endemics do ; the other based on the local distribution of the highly 
modified Tristichaceae and Podostemaceae and the cosmopolitan distribu- 
tion of the little modified forms. 
Mr. Ridley’s objections to the mutation theory are then considered, 
and it is shown that the supporters of Natural Selection do not clearly 
distinguish between post hoc and propter hoc . Natural Selection cannot 
explain the origin of the peculiarities which distinguish plants, but can 
only preserve or destroy them when once formed. The reply of the 
Natural Selectionist to queries invokes incomprehensibility, as did formerly 
that of the Special Creationist. 
Finally a list ^is given of factors which may modify the action of 
my law of age and area. 
Literature quoted. 
1. Ridley, H. N. : Endemism and the Mutation Theory. Ann. Bot., vol. xxx, 1916, p. 551. 
2. — : On the Dispersal of Seeds by Wind. Ann. Bot., vol. xix, 1905, p. 351. 
3. Thwaites, G. H. K. : Enumeratio Plantarum Zeylaniae. London, 1864. 
4. Trimen, H. : Flora of Ceylon. London, 1893-1900. 
5 . Willis, J. C. : The Endemic Flora of Ceylon. Phil. Trans., B, vol. ccvi, 1915, p. 307. 
6. : The Evolution of Species in Ceylon, with reference to the Dying Out of Species. 
Ann. Bot., vol. xxx, 1916, p. 1. 
7. . The Distribution of Species in New Zealand. Ann. Bot., vol. xxx, 1916, 
P* 437- 
