213 
Willis . —Age and Area. 
imagined (for example, there might have been invasion from the direction of 
St. Alban’s Head, as shown in the third circle), so that this is really only 
a rough approximation. But on this basis let us see to what extent the 
flora of Dublin is predicted. The flora is helped out in a few instances by 
that of Wicklow and Wexford, especially in regard to mountain species. 
Taking from Watson those plants that fulfil one or other of the two 
conditions laid down above as needful, one obtains a total of 739 species. 
Many of these are now regarded as aliens or introductions of some kind, 
and it would lead too far to go into the question in detail. Of these 739 
our region includes 564 regarded as fully native, or 72 per cent. A further 
47 (6 per cent.) are marked by Colgan as colonists, but all of them except 
Anthemis arvensis are marked in the ‘Cybele Hibernica’ as native in Ireland. 
Still another 49 occur in Dublin, marked by Colgan as Casuals, Denizens, 
or Aliens, and the Cybele marks 27 of these as native in Ireland. We thus 
find in all, 564 + 46 + 27 = 637 out of 739, or over 86 per cent., predicted. 
Of the remaining 102, the Cybele gives 45 as native in parts of Ireland, so 
that only a few plants remain that are not found. Of the species found in 
Dublin, and not predicted, 40 in all, 12 are marked by Colgan as Aliens, 
Casuals, or Colonists, Considering the effects of man’s occupation for so 
many centuries, this result must be looked upon as very successful 
prediction. 
One may even apply prediction nearer home. A circle with centre at 
the South Foreland, and including Dorset, also includes much of Derby¬ 
shire, and one will therefore expect a great similarity between the floras of 
these two counties. Taking the floras of Mansell-Pleydell and of Painter, 
and comparing, one finds the species the same for page after page, the two 
counties having no less than 1,305 in common, i.e. 88 per cent, of the flora 
of Dorset, and 95 per cent, of that of Derby. Of the remainder of the 
Dorset flora, 84 are seacoast species, which one will not expect to find in 
Derby, and in Derby 23 are Highland types that cannot occur in Dorset. 
If we omit these from the respective floras, the 1,305 species in common 
represent 93*2 per cent, of the flora of Dorset and 97*2 of that of Derby. 
A more detailed study of invasions, and of local distribution in England, 
would probably make the approximation even closer ; this is merely given 
as a rough illustration, and was chosen simply because I happened to have 
at hand the flora of Derbyshire. 
A Correction of Previous Work upon the Flora of Ceylon. 
Mr. J. S. Gamble, C.I.E., F.R.S., informed me in conversation that in 
the course of his work upon the flora of Madras, a number of species had 
been discovered there which in my Catalogue of Ceylon Plants are recorded 
as endemic to Ceylon. It at once struck me that upon the theory of Age 
