CH. VI] AGE AND AREA 57 



(approximately) in the case of a few VR species, which occur 

 together on the same mountain-top. The VR species that occur 

 m the large forests have each their own location. Noav a little 

 consideration will soon show that from the point of view of 

 evolution to suit local conditions this is a very remarkable state 

 of affairs. It is of course obvious that if a species newly evolved 

 upon a small area does not suit the conditions that obtain upon 

 that area at the time in ■which it was evolved, it Avill be promptly 

 killed out; but while this is so there is no actual need to imagine 

 that it was evolved specially "adapted" to those conditions. 



If two species A and B grow in overlapping areas, both must 

 be growing in the coincident portion; and what keeps A from 

 growing into the rest of B's territory, and D into ^'s? It has 

 usually been insisted that it was because A was adapted to its 

 own territory, and B to its own. But when one considers that 

 the conditions are never the same from one spot to the next, 

 nor from one year to the next, this would mean a most wonderful 

 adaptation if the species were not to grow into each other's 

 territory, especially when one remembers the many more widely 

 distributed species that occur in both. In reality the case is 

 more complex, for there are at least a dozen overlapping at any 

 one point, while in Ceylon the soil is essentially the same through- 

 out the greater part of the island, the flora was practically "all 

 forest before the arrival of man, and the rainfall varies very 

 much from year to year in quantity and distribution. It was 

 evident that the old ideas of particular adaptation were un- 

 tenable, and this view was enormously strengthened by subse- 

 quent discovery of the way in which species were grouped in a 

 country. 



This conclusion was confirmed by later work on the Podo- 

 stemaceae (124), a family of water-plants of smooth rocks in 

 rushing tropical and subtropical mountain streams only. Here 

 there is nothing to which the many genera and species can be 

 adapted, for the conditions are the same for all, and could not 

 be equalled for uniformity in a laboratory of the temperate zone. 

 They grow only upon a smooth rigid substratum, from which 

 they take no food; all grow in water, and have no climatic 

 differences, no difference in circumambient medium, in light, or 

 in any other factor. And yet there have evolved many genera 

 and species, with very striking and bizarre differences between 

 them. Evidently it is not necessary to ha\e local condi- 

 tions to which to be adapted in order to ensure that evolution 



