Further Evidence for Age and Area; its Applicability 
to the Ferns, &c. 
BY 
J. C. WILLIS, M.A., Sc.D. 
W HEN once the regular graduation of species in a genus or family 
into series of what we may almost perhaps term ‘wheels within 
wheels ’ (10, figs. pp. 336 - 7 ) has been pointed out, it needs but little investi- 
gation to convince oneself that the law of ‘ age and area ’ is general in its 
applicability. So long as it was only based on the estimates made by 
Trimen for the Ceylon flora, its foundations were by no means secure, but 
it was soon confirmed to a high degree of certainty by the results for the 
flora of New Zealand (9), where actual measurements of range were em- 
ployed. Perhaps the most striking proof of the probable correctness of my 
deductions is the remarkable result given in Tables III to VI of that paper. 
The further investigation of the outlying islands of New Zealand (15) showed 
the operation of the law even more decisively if possible, at the same time 
giving what appears to me a fairly conclusive proof that the active factor in 
distribution is age (not youth) within the country. 
It would therefore seem that the production of a few more pieces of 
confirmatory evidence, based like the figures for New Zealand upon actual 
measurements, should suffice to establish the hypothesis upon a firm basis. 
In the present paper I give five such pieces of evidence, three of which at 
the same time go to show that the hypothesis applies not only to the 
Angiosperms, to which alone I have confined it as yet, but also to the 
Coniferae and Ferns, and is therefore probably perfectly general in its 
application. 
It is not usually possible to get such clear and convincing evidence as 
shows in the floras of Ceylon and New Zealand, where the plants can be 
split into three sections, graduated in order of rarity (Ceylon, Ceylon- 
Peninsular India, Wide ; New Zealand, New Zealand and outlying islands, 
Wide), though the first and fourth cases given here are such. But once the 
graduation is seen to hold generally, it will suffice to parallel them in one 
or more features. 
[Annals of Botany, Vol. XXXI. Nos. CXXIII and CXXIV. July and October, 1917.] 
