On the Law of Age and Area, in Relation to the 
Extinction of Species. 
BY 
AGNES ARBER. 
D R. J. C. WILLIS, in the well-known series of papers in this and other 
journals in which he has elaborated his theory of ‘ Age and Area 
has brought forward evidence for its validity which appears to me to be 
completely convincing. I am, however, unable to accept one subsidiary 
hypothesis, which Dr. Willis seems to regard as an integral factor in his 
scheme — the idea that, at least in the case of the Angiosperms, no extinc- 
tion of species is now proceeding. This opinion he has repeatedly expressed. 
He wrote, for instance, in 1916 1 that ‘There is no evidence whatever that 
any of the angiospermous species of the Ceylon flora are dying out, and 
from analogy we may imagine this to be generally true ’. He does indeed 
qualify this in 1918 2 as far as to admit that ‘ there is a certain amount of 
geological evidence of former greater spread ’, but he seems to regard this 
as an exception of no real importance. Berry, 3 on palaeobotanical 
grounds, and also Sinnott 4 and Ridley, 5 for more general reasons, have 
controverted Willis’s view that no extinction is taking place among the 
Flowering Plants, and have expressed the opinion that certain members of 
this group are dying out at the present day. 
When we look at the matter broadly, and consider living things as 
a whole, it becomes abundantly clear that extinction both of plant and 
animal species has occurred on a vast scale in the course of bygone 
geological epochs. I fancy that those palaeontologists who have paid the 
closest attention to these questions would be the least likely to accept 
Willis’s contention that extinction in the past has been due almost entirely to 
catastrophes of some kind, or to great climatic changes. 6 Even if we follow 
Willis in narrowing the issue down to Angiosperms, we must admit that 
there is no apparent reason for supposing them privileged to escape the 
universal fate. It might possibly be maintained that at the present day 
the Angiosperms are a dominant group entirely on the up-grade, in which 
extinction has not yet begun. But this position is refuted by certain 
1 Willis, J. C. (1916). 2 Willis, J. C. (1918). 2 Berry, E> w> (1917 
4 Sinnott, E. W. (1917). 5 Ridley, H. N. (1916). « Willis, J. C. (1918). 
[Annals of Botany, Vol. XXXIII. No. CXXX. April, 1919.] 
