212 
Sinnott . — The ‘ Age and Area ’ Hypothesis 
element in a flora is its youngest element, consisting of species which have 
recently been developed, each in a definite locality, and which have as yet 
not had time to extend their ranges widely. The non-endemic types he 
looks upon as the oldest element, the first invaders of a region from abroad 
which have had time to become widely distributed and common. 
This idea that endemics are always young species is open to two 
objections. First, it disregards the evidence that many endemics are not of 
local origin but are ‘ relicts ’, ancient types which were formerly widespread 
but which now survive only in isolated corners of the world. We are 
familiar with many species the range of which is widely discontinuous ; for 
example, that interesting group which is to-day confined to Eastern Asia 
and to a small area in the south-eastern United States, or that group of 
antarctic species many of which are also found near the Arctic Circle but 
nowhere between. In such cases we are driven to the conclusion that these 
plants were once much more widely distributed, and that if extinction should 
progress a little farther they would survive in only one of their two present 
homes. They would then constitute a part of its ‘ endemic ’ flora, but would 
obviously not be of recent and local origin there. Many of the species and 
genera in Ceylon have to-day a discontinuous distribution similar to that 
which we have mentioned. They find their co-types or their nearest relatives 
in the Himalayas, perhaps, in the Malay Peninsula, in East Africa, or in 
Australia. Many New Zealand species, in the same way, are identical with 
or closely resemble others found in Patagonia, South Africa, Hawaii, or 
other distant places, and nowhere else. Such types certainly have the 
appearance of being remnants of species and genera once much more widely 
spread, in which a little more ‘ dying out ’ would result in the production of 
forms definitely endemic in one of their present areas. The conclusion is 
hard to escape that certain of the Ceylon and New Zealand endemics have 
had such a history. To imagine the monotypic endemic genera, at least (of 
which there are many), as having arisen by a single leap is to tax heavily the 
imagination of even an ultra-mutationist. 
Another objection to the conclusion that endemics are always of recent 
development is the fact that in the floras under discussion, and other ancient 
ones, the endemics include a very much higher percentage of trees and 
shrubs than do the non-endemics. In a former paper by the writer and 
Professor Bailey 1 it was shown that in Ceylon the non-endemic species (accord- 
ing to Willis the ancient stock of the island from which the endemics have 
developed) included only 55 per cent, of trees and shrubs ; whereas of the 
endemic species, 77 per cent, belonged to these woody growth forms. In 
New Zealand, in the same way, only 19 per cent, of the non-endemic 
species are woody, but 49 per cent, of the endemics. This rarity of trees 
1 Sinnott, E. W., and Bailey, I. W. : The Origin and Dispersal of Herbaceous Angiosperms. 
Ann. of Bot., vol. xxviii, 1914, p. 547. 
