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and the Problem of Endemism . 
The chief argument on which the hypothesis is based is the fact, which in 
the face of the data presented cannot well be doubted, that endemic types 
have comparatively narrow ranges and non-endemic types comparatively wide 
ones. To a certain extent, particularly in genera which are rich in endemic 
species and which seem to be developing new forms rapidly, such as Impatiens , 
Eugenia , and Strobilanthes in the Ceylon flora, this restricted dispersal 
among the endemics is doubtless due in part to their youth. In many cases 
it may also be due to the fact that a given species is a tree and therefore 
slow to spread. The belief is hard to escape, however, that very many 
endemics owe their limited distribution to the circumstance that they are 
remnants of comparatively unsuccessful types which have been exterminated 
elsewhere and which even in these isolated floras are waging a losing fight 
against more vigorous and adaptable new-comers. In previous publications 
the writer has stated his conviction that in ancient insular floras and those 
of the great land masses of the Southern Hemisphere the endemic element 
is in general more ancient than the non-endemic, and he sees no reason to 
modify this belief ; for endemics are either ‘ relicts ’ and thus very ancient, 
or else they represent types which have been in the region long enough so 
that their original characters have been lost. The hypothesis which perhaps 
seems to fit best all the facts at hand regards isolation as a factor which 
tends not only to develop new species but also to modify and extinguish 
old ones ; and hence looks upon species in Ceylon and New Zealand which 
still maintain specific identity with their co-types on the mainland as the 
newest arrivals rather than as the most ancient members of the flora. 
The whole problem of endemism is exceedingly complex. We must 
recognize that there exist two widely different types of endemic forms — 
‘ relicts ’ and ‘ indigenes ’ ; we must recognize that species differ in their 
adaptability and competing power and in the rapidity with which they may 
extend their ranges, and that these factors are very important in determining 
whether a plant shall be local or widespread ; we must recognize that 
certain types are phylogenetically younger than others and that their 
distribution is accordingly affected ; and we must recognize that plant types 
differ widely in the rapidity with which they produce new species, and hence 
in the rapidity with which an endemic element will arise among them. The 
purpose of the present paper is to point out certain of these complexities and 
to show that no single hypothesis like that of ‘age and area’, however 
valuable it may be in explaining certain facts, can be used as a key to the 
whole problem. 
Summary. 
i. Dr. Willis’s ‘age and area’ hypothesis assumes that the area 
occupied by a species depends primarily upon its age (the older the species, 
the wider its range) ; and that ‘ dying out ’ of species occurs very rarely. 
Q ^ 
