November 5, 1915] 



SCIENCE 



651 



may have been the cultures due to incomplete 

 germination. One can not feel confident that 

 the results were more than glimpses of the 

 genetieal possibilities and under these condi- 

 tions speculation loses its point. We are not 

 likely to be in a position to discuss satisfac- 

 torily the problems of CEnothera genetics until 

 new series of experiments are undertaken with 

 methods whereby the germination of seeds is 

 forced to a finish. 



Gates makes an attack on the extreme views 

 of certain Mendelian writers who have held 

 so strongly to a principle of the conservation 

 or fixity of factors that they do not allow of 

 their modification even through crossing. It 

 may be doubted whether this group of Men- 

 delians is really a large one, but so far as they 

 do exist the criticisms of Gates are likely to 

 have the sympathy of his readers. It is, bow- 

 ever, one thing to recognize the complexity 

 and possible instability of protoplasm as to 

 its stereochemistry and quite another to hold 

 that stereochemical changes within a pure spe- 

 cies can produce such great modifications of 

 morphological structure as the mutationists 

 would have us believe. And the Oenotheras are 

 so strongly under suspicion of genetic com- 

 plexity through hybridism that we have a right 

 to expect that evidence for mutation from this 

 group will be most critically sifted and only 

 employed where it is found in material of 

 proven purity. 



One may be Mendelian, firmly believing in 

 the principle of segregation following an F, 

 generation which is the principal tenet of Men- 

 delism, and still admit the probability of modi- 

 fications from time to time of the stereochem- 

 istry of germ plasm even in so-called " pure 

 lines." That such changes may result in spon- 

 taneous modifications of structure seems rea- 

 sonable on philosophical grounds and such 

 modifications would constitute mutations since 

 they are discontinuous. But it remains to be 

 proven that such modifications affect changes 

 in morphology to the degree claimed by the 

 mutationists, although it may well be possible 

 that numerous small mutations would in time 

 have a cumulative effect readily recognized. 

 Thus advances in evolution may come about 



through numerous small steps, as held by 

 Darwin, and some of these may be mutations, 

 but it seems probable, as so strongly argued by 

 Weismann, Lotsy and others, that the chief 

 causes of variation in higher animals and 

 plants and the most important directions of 

 evolution are determined through the mixing 

 of diverse germ plasms with their complex 

 interactions. Modifications of germ plasm 

 through crossing, and mutations due to ex- 

 ternal chemical and physical factors, would be 

 expected at times to work simultaneously, and 

 in such cases it may become a difficult matter 

 to distinguish their separate effects. Muta- 

 tions even though small in degree would, how- 

 ever, if sufficiently numerous, work in time 

 profound modifications of structure, and on 

 this common ground the mutationists and the 

 followers of Darwin seem to have the strongest 

 hopes of reaching an agreement. 



The final chapters, " A General Theory of 

 Mutations " and " The Evolutionary Signif- 

 icance of Mutations," continue and elaborate 

 the discussion which runs through the previous 

 pages and thus largely summarize or expand 

 the author's views. A bibliography of about 

 500 titles, of which 42 are by Gates, completes 

 the work. 



Bradley M. Davis 



A Text-hooh of Zoology for Universities, Col- 

 leges and Normal Schools. By Thomas 

 Walton Galloway, Ph.D., Litt.D., Pro- 

 fessor of Biology in the James Millikin Uni- 

 versity. Third edition, revised. P. Blakis- 

 ton's Son & Company, Philadelphia. 

 It fell to the lot of the present writer to 

 undertake a review of the first edition of this 

 book^ which was published in 1906. In paper, 

 typography, binding, etc., the book is well made 

 and attractive to look upon, a very deserved 

 compliment to the publishers, who seldom 

 allow anything inferior in the way of book- 

 making to emanate from the house. 



Intrinsically there is little change over the 



first edition, aside from the addition of some 



four chapters comprising about sixty-five pages 



more than the former book. The same plan 



1 Science, Vol. XXIV., p. 719. 



