518 Guppy . — Testimony of the Endemic Species of the Canary 
But the most significant fact in this connexion is that when Dr. Willis 
first promulgated his theory of Age and Area (‘Ann. Roy. Bot. Gard. 
Peradenya’, May 1907) his preliminary statement of it took this form. 
When he came to elaborate it he gave it the name of its most striking 
implication, Age going with Area. He arrived independently at the same 
conclusion respecting the plant-stocking of Ceylon and the adjacent 
mainland that botanists a generation ago had framed in the case of genera 
of the Pacific Islands. We have been apt to forget this preliminary 
statement of his position ; but it is the essence of his theory. His views 
on the local origin of endemic species were first presented in this form : 
‘ The general principle on which India and Ceylon have been peopled 
with the many species which they contain would seem to be that one very 
common species has spread widely, and so to speak shed local endemic species 
at different points, or else that one species has spread, changing at almost 
every point into a local endemic species, which has again changed on 
reaching new localities.’ Examples are given of Clematis and Anemone 
in the Himalayas (we are told that many more cases could have been cited), 
where we have associated with a single species ranging throughout the 
region various allied species confined to particular localities. When 
Dr. Willis asked how these cases could be explained ‘ but on the parent 
and child theory ’ he put a question which many of us have asked. 
But this principle is not merely insular. It is, as we have seen in the 
case of the Indian mainland, also continental. Whilst the highly variable 
species may cover much of a continent, its derivative species are restricted 
to small areas. Few better examples could be given than those of different 
species of Geranium over great areas of the Eurasian steppes, in the 
highlands of Mexico and Central America, over the length and breadth ot 
the Andine region, and in the high mountains of the breadth of tropical 
Africa. The role of the wide-ranging polymorphous species, as a parent 
of localized endemic forms, has been as effective in the great mountainous 
regions of the continents as it has been over the archipelagos that dot the 
oceans. (As concerns Geranium the subject is lucidly treated by Knuth in 
his monograph on the Geraniaceae, 1912, one of the Pflanzenreich Series, 
PP- 79. % 8 5, 175, 185, 196, 203.) 
It may be remarked in conclusion that of the several eminent botanists 
cited above not one could have been cognizant of any such theory as that 
of Dr. Willis. They have been named here in connexion with the 
important part played by the highly variable wide-ranging species in 
distribution, and it is on the behaviour of these polymorphous species that 
Dr. Willis based the preliminary statement of his views on the local origin 
of endemic species. His principle was often implied in the practice of these 
systematists, though not as an integral principle, but as part of a code that 
was none the less valuable because it was often unwritten. In theory a few 
