CH. xiii] D. GEOGRAPHICAL DISTRIBUTION 147 



tropical Africa or America. But on averages there are very great 

 differences between the species of the three groups, and the 

 statement above made as to relative distribution is fully borne 

 out in all cases that have been investigated. Between the widely 

 distributed species and the local endemics in New Zealand, there 

 is a great difference in range (average length for wides 742 miles, 

 for endemics 414). 



On the theory of natural selection, it is quite impossible to 

 make any prediction about what is likely to be found in studying 

 the distribution of plants in such a place as Ceylon. The sup- 

 porters of that theory tried to answer the author's attack by 

 calling in two supplementary hypotheses, which as already 

 shown (p. 24) are mutually contradictory. The Ceylon local 

 species were supposed in the first to be local adaptations to the 

 Ceylon conditions. But this did not get over the difficulty of the 

 intermediate distribution of the species that also occurred in 

 South India. Were they suited to the conditions that occurred in 

 both countries, and if so what were those conditions, and how did 

 natural selection adapt plants in such a way that some Ceylon 

 things were confined to Ceylon, some reached as far as say 

 Cochin in South India, while some got as far as Goa and some to 

 Bombay? This overlapping of areas, which shows in all parts of 

 the world, is a fatal objection to the theory of local adaptation as 

 a general rule for the explanation of endemics, without something 

 else to explain the varying distribution that they show. But in 

 any case, it was a very remarkable thing that if they were really 

 local adaptations to local conditions, they should be the rarest 

 plants in those very conditions. Their general distribution was 

 simply a reproduction on a smaller scale of the kind of distribu- 

 tion that might be seen in any big genus or family, or in the 

 flora of any big country — all gave the same "hollow" curves. 

 There was nothing peculiar about local endemism to distinguish 

 it from any other type of distribution. 



The rival supplementary hypothesis, which contradicts the 

 first, and is the popular explanation at the present time, is that 

 the endemics of a country are the relics of a previous vegetation. 

 The tenacity with which this opinion is held, in spite of all 

 evidence to the contrary, is really noteworthy, though a weakening 

 is to be seen in the tendency to expand the idea of a relic. Such 

 things as Ceanothus in North America may perhaps be brought 

 into this category, though the genus has about forty species, 

 which puts it very definitely into the large genera, but it does. 



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