348 Willis . — Further Evidence for Age and Area; 
endemic. Didymocarpus Perdita , Ridley, perhaps belongs to this class. 
Mr. Ridley ( 7 , p. 555) collected two specimens, and the species has never 
been seen again ; probably he exterminated it in its earliest stages. 
Christisonia albida , Thw., found (once only) at Hakgala in Ceylon, has never 
been seen again, though there is a botanic garden there, and the forest has 
been most carefully ransacked. Thwaites describes it as white, so that 
perhaps it was weeded out by Natural Selection for lack of the brownish 
colouring matter of its family, and yet it was so different in other features as 
well that Hooker accepted it as a Linnean species. 
Once this early stage is passed, my work on age and area goes to show 
that the further distribution of species depends on their mere age far more 
than on any other factor. 
But the species which are thus found commencing, and which have 
apparently passed through the Natural Selection sieve, are not, in the great 
majority of cases, distinguished from their congeners of the same country 
simply by small and unimportant differences, but by well-marked characters, 
which very often are sufficiently numerous and well defined to rank the 
species as Linnean. 
In the case of Coleus elongatus , for example, the species is distinguished 
from C. barbatus, its nearest relative, and from all other species of Asia, by 
the peculiar raceme-like inflorescence, and by the five equal teeth of the 
calyx, in place of the one large upper and four small lower teeth of other 
Colei. 
Unless, therefore, evidence can be brought up to prove that such species 
have arisen by the dying out, or the killing out, of intermediate forms, there 
seems nothing for it but to admit that considerable mutations may take 
place. In numerous cases, too — for instance, ColeJis elongatus — intermediate 
stages are not possible, so that probability goes against supposition of the 
dying out of intermediate forms. In any case, ‘age and area’, taken together 
with previous work, speaks very strongly in favour of mutation as the 
immediate means by which new species have arisen. 
Summary. 
Five further pieces of evidence are given, confirming, and extending 
the application of, the hypothesis of age and area. 
The range of the Orchids of Jamaica is shown to go in the order — 
endemics least, Jamaica-Cuba species next, wides greatest. 
The flora of Hawaii is shown to be easily explicable on the same 
hypothesis, the wides ranging much more than the endemics, which are 
graduated down to a maximum (in one island only). 
Calliti'is is taken as an example to show that Coniferae are also included 
in the operation of the law. 
