448 SCIENCE PROGRESS 



endemic Angiosperms, in much the same way as it is shown 

 to have done between the dispersal of the non-endemic and 

 that of the endemic Angiosperms. 



The same points are brought out in the fifth essay, a study 

 of the distribution of the ferns of the Hawaiian Islands. The 

 endemic ferns again occupy a greater area than the endemic 

 Angiosperms and a lesser area than the non-endemic ferns. 

 The non-endemic ferns, as in New Zealand, occupy on the 

 average about the same area as the non-endemic Angiosperms, 

 a fact which Willis explains by the constant arrival of non- 

 endemic species of ferns on account of the easy dispersal of 

 the latter by means of their spores. 



Another supporter of natural selection, Copeland (i), main- 

 tains that age has been previously recognised as a factor in 

 distribution, and that " mutation " is merely another word for 

 " variation." Like Ridley, he fails entirely to discriminate 

 between continuous and discontinuous variation. Indeed, 

 mutation or discontinuous variation has taken so great a place 

 in evolutionary facts that adherents of natural selection seem 

 to accept them, unconsciously admitting the facts upon which 

 de Vries founds his theory while nominally in opposition to 

 the theory itself. This is obvious in the following quotation 

 from Copeland, " Regarding myself as a confirmed adherent 

 of the doctrine of natural selection, I do not hold it in the 

 slightest measure directly responsible for the origin of any 

 species. Species originate by variation. There is not the 

 slightest doubt that in nearly all cases . . . variation is indis- 

 criminate in direction." 



In a series of appreciative reviews de Vries (3-5) empha- 

 sises the point that " a general cause must govern this 

 phenomenon, a cause which is, at any rate, independent of 

 morphological and biological qualities," and concludes that 

 the " age and area " theory is the only one sufficiently broad 

 to explain all the facts. 



Other reviews in sympathy with the theory have appeared, 

 one by Lotsy (6) and another by Coulter (2) which, if somewhat 

 non-committal, is not in strenuous opposition like those of 

 Ridley and Copeland. Indeed, Coulter and various other 

 eminent American botanists are quite in sympathy with the 

 new doctrine which will, no doubt, take its proper place in the 

 study of geographical distribution. 



