No. 614] FACTOR MUTATIONS IN EVOLUTION 127 



preserved they give rise to new forms or races, and when 

 fostered by man they make possible new horticultural 

 varieties of plants or new breeds of animals. It is prob- 

 able, as Morgan has shown, that factor mutations alone 

 have furnished the necessary germinal changes to make 

 possible the evolution of the elephant's, trunk and similar 

 cases of orthogenetie development which have been dis- 

 covered by paleontologists. But factor mutations alone 

 are not sufficient, so far as we know, to account for the 

 origin of species of different chromosome numbers, much 

 less for the appearance of phyla and genera. It is to be 

 hoped that light will be shed on these more obscure phases 

 of the general problem of organic evolution through a 

 combination of taxonomic, genetic, cytological and physio- 

 logical researches. It would seem that the solution must 

 involve the expression of relationships between organic 

 groups in terms of the morphology and physiology of 

 the chromosomes. 



LITERATURE CITED 



1916. Studies in Juglans, III; Further Evidence that the Oak-like 

 Walnut Originates by Mutation. Univ. of Calif. Pub. in Agr. 

 BcL, 2, pp. 71-80. 

 Bateson, Wm. 



1914. Address of the President of the British Association for the Ad- 

 vancement of Science. Set., N. S., 40, pp. 287-302 ; 319-833. 



Caullery, M. 



1916. The Present State of the Problem of Evolution. Set., N. S., 43, 



Clausen, R. E., and Goodspeed, T. H. 



1916. Hereditary Reaction System Relations— an Extension of Men- 

 delian Concepts. Proc. Nat. Acad. Sci., 2, p. 240. 

 Davenport, C. B. 



1916. The Form of Evolutionary Theory that Modern Genetical Re- 

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Glaser, O. C. 



1916. The Basis of Individuality in Organisms. Sci., N. S., 44, pp. 

 219-224. 



Goodspeed, T. H., and Clausen, R. E. 



1917a. The Nature of the F, Species Hybrids between XU-otinnti s,/l- 

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 Heredity. Univ. of Calif. Pub. Bot., 5, pp. 301-346. 



