Species and other Controversial Points. 191 
a change of o*i in the rarity of the endemics and the Ceylon-Indians, which 
makes no difference to their validity for my argument. 
Mr. Ridley further goes on to state that future work on the Ceylon 
flora will so modify the results obtained from Trimen that any deductions 
based upon the latter will be valueless. I have already shown how little 
difference Trimen’s work made in Thwaites’s results. My own made still 
less in Trimen’s, and the differences will decrease as time goes on. As I 
have already stated, the effect of the completion work, when once a flora, 
like that of Ceylon or New Zealand, is reasonably well worked out, is to add 
new species to the class VR, to move a few VR into R, rather fewer R into 
RR, and so on in decreasing proportions up the scale. But this leaves the 
ultimate result the same as before. 
In any case the Ceylon figures, estimates though they be, are shown to 
be fairly accurate and reliable by the fact that they come out with such 
arithmetically regular gradations along the scale in opposite directions for 
endemics and wides ; and this is amply confirmed by the fact that the New 
Zealand figures, which give actual measurements, agree with them. 
I much regret that in my Ceylon papers I did not make sufficiently 
clear the various conditions that might modify the action of my age and 
area rule. Partly this was because I thought that many were obvious, and 
partly because I was thinking more of making the law itself clear. In later 
papers I have instanced various such conditions, and Mr. Ridley’s paper is 
also of great service in this respect. In the New Zealand paper ( 7 ), p. 449, 
I have said that ‘ the vast flora of introduced weeds may be left out of 
account, for there is not the least evidence to show that they would have 
spread had not foreign conditions , or disturbance of the native conditions, 
been also introduced ’, whilst in a paper which I read to the Linnean Society 
last year I went into this question in detail, analysing the flora of introduc- 
tions into Ceylon which I have elsewhere published (8). This list contains 
387 plants, and I showed that there was no evidence of spread without 
alteration of conditions except in four cases. Here the spread is but small, 
and in at least two has been indirectly assisted by man. 
It is evident that if man arrive in a country and make extensive 
clearances, allowing the spread of introduced weeds like the lalang (cf. 1, 
p. 572), the operation of my law of age and area must be interfered with. 
For this reason, remembering how much of ‘dry’ northern and eastern 
Ceylon was once occupied by agriculture, I do not think that the detailed 
list of its flora as now made up is very complete, though, owing to the con- 
figuration of the island, and the direction of the. monsoons, I cannot for one 
moment admit that this country was ever covered with ‘ wet-zone ’ forest. 
Even there, however, there was a good deal of forest left, while the bulk of 
the Ceylon flora, whether ‘ wide ’ or endemic, lies in the south-west, which 
at the time of Thwaites was comparatively little encroached upon. 
