2 1 4 Sinnott . — The ‘ Age and A rea ’ Hypothesis 
occurrence, for the very many species, genera, and families among the 
Angiosperms which are isolated in distribution and in relationships can only 
be explained (unless we are extreme mutationists) by assuming an enormous 
amount of extinction to have occurred in the past. 
But extinction in this sense seems not to be the only way in which 
species die out. Dr. Willis believes that the present endemic floras of 
Ceylon and New Zealand have been developed from species of early arrival 
in those regions from India and Australia, species which now form the non- 
endemic and most common element in their respective floras. In the case 
of Ceylon, however, there are no less than sixty-three genera among the 
Dicotyledons alone, or 8 per cent, of the whole, which, though not endemic 
in Ceylon, are represented only by endemic species. Dipterocarpus , Shorea i 
Hopea, Xylopia , Euonymus , Gym nostachyu m , Actinodaphne , Lasianthus , 
Mangifera , Semecarpus , and others are examples. In New Zealand ninety 
non-endemic genera of Dicotyledons, or 43 per cent, of the whole, are 
similarly represented only by endemic species, and among these genera are 
some of the most important in the islands. In these cases, where is the 
parent species or group of species in each genus which has supposedly given 
rise to all these endemic forms and which should now be Very Common ? 
If it has not ‘ died out what has become of it ? The fact that the propor- 
tion of such genera (not endemic but containing only endemic species) is 
lowest in those regions where the arrival of new species has apparently been 
of frequent occurrence, and highest in regions which are most isolated, 
suggests that these parent species tend eventually to disappear altogether. 
As to what happens to them we cannot be sure. Some may simply be 
exterminated outright and some, by continual crossing with new forms, may 
ultimately lose their specific identity. We are tempted to believe that the 
longer a successfully invading species remains in an isolated area like Ceylon 
or New Zealand (after its first rapid spread) the less common it tends to 
become until it is actually ‘ swamped ’ out of existence — quite the reverse of 
the ‘ age and area ’ idea. 
Certain minor objections may be urged against Willis’s conclusions, such 
as, first, that the great majority of endemic types in Ceylon are on the 
southern end of the island instead of the northern, the point nearest the 
bridge to India, where they should be according to analogy from his 
arguments as to New Zealand ; and, secondly, that the flora of New Zealand 
was in all probability derived not only across a northern bridge from 
Australia but also, in large part, across a southern bridge from Antarctica 
at the time of the northward migration of the ‘antarctic’ flora. This fact 
should result, according to the hypothesis in question, in the concentration 
of a much larger number of species at the southern end of the South Island. 
There is doubtless much truth in Willis’s main contention that, other 
things being equal, the longer a species lives, the wider the range it will cover. 
