The Geographical Distribution of the Dilleniaceae, 



as illustrating the Treatment of this Subject 



on the Theory of Mutation. 



BY 



J. C. WILLIS. 



MY choice of an order was deterrained by the fact that this 

 was the first order in Hooker's Flora of British India 

 with other than world-wide distribution. 



In previous papers* I have given arguments in favour of the 

 mutation theory that seem to me sufficient justification for 

 accepting it as a working hypothesis, and testing whether it 

 breaks down when appHed to the actual facts of any subject. 

 For absolute proof we require of course to show in a few cases 

 at any rate that actual mutation has occurred. I have a 

 number of experiments on hand, in which, by growing plants 

 under different climates, under radio-activity, on the clinostat, 

 and in other ways, I am endeavouring to produce mutation, 

 but these must m any case occupy some years, and it will be 

 worth while testing the theory, as that of evolution itself was 

 tested, by working out various problems assuming it to be true. 

 The one which has most interested me is that of geographical 

 distribution, but there are many other directions in which the 

 acceptance of mutation will produce far-reaching results. 



If we examine the local distribution of the Dilleniaceae in the 

 East, we find that in the larger genera— and this is the case with 

 any of the larger genera, of any order that I have examined — 

 there is a general tendency for there to be several local endemic 

 species, connected by one or two widely ranging common 



* Willis, Some Evidence against the Theory of the Origin of Species 

 by Natural Selection of Infinitesimal Variations, and in favour of Origin 

 by Mutation. Ann. Perad., IV., 1907. p. 1. Further Evidence, &e., 

 Ann. Perad., IV., 1907, p. 17, 



[Annals of the Royal Botanic Gardens, Peradeniya, Vol. IV., Part II., October, 1907.] 



