Maech 20, 1903.] 



SCIENCE. 



445 



classes must be sharply separated when evo- 

 lution questions are discussed. Nearly ten 

 years ago I endeavored to combat the 

 species-dogma from the garden point of 

 view, as, in differing ways, others had done 

 before ('Survival of the Unlike,' Essay 

 IV.). The confusion of the two concep- 

 tions expresses itself in the terminology of 

 plant-breeding. Some writers define hybrid, 

 for example, as a cross between species ; this 

 is the classificatory idea. Others define it 

 to be any cross. The former use of the word 

 is the more proper merely because it is the 

 historic use, originating as a systematist 's 

 concept. The latter idea should have been 

 expressed by a new word. It is for this 

 reason that I have held to the old or sys- 

 tematic definition of hybrid; but there is 

 no appeal against usage, so, while still pro- 

 claiming the righteousness of my cause as 

 an easement of my conscience, I strike my 

 colors and henceforth use the word hybrid 

 for a cross of any kind or degree. How 

 often does mere language confuse us! 



From an argumentative point of view, it 

 will be difficult to determine, in a given 

 case, just what are variations and what 

 mutations, for these categories are sepa- 

 rated not by any quantitative or qualitative 

 characters— the 'step' from one to the 

 other may be ever so slight— but by the 

 test that one kind is fully heritable and the 

 other only partially so. If a mutation is to 

 be defined as a heritable form, then it will 

 be impossible to controvert the doctrine 

 that evolution takes place by mutation, be- 

 cause the mutationist can say that any 

 form that is inherited is by that fact a 

 mutation. This will be equivalent to the 

 position of those who, in the Weismannian 

 days, denied the transmission of acquired 

 characters, but defined an acquired char- 

 acter to be one that is not transmissible. 

 However, it is to be hoped that the dis- 

 cussion of the mutation theory will not 



degenerate into a mere academic debate 

 and a contention over definitions. Pro- 

 fessor De Vries has himself set the direc- 

 tion of the discussion by making actual ex- 

 periments the test of the doctrine. There 

 will be confusing points, and times when 

 we shall dispute over particular forms as 

 to whether they are variations or muta- 

 tions ; but every one who has studied plants 

 from the evolution point of view will be 

 prepared to believe that species do originate 

 by mutation. For myself, I am a Darwin- 

 ian, but I hope that I am willing to believe 

 what is true, whether it is Darwinian or 

 anti-Darwinian. My own belief is that 

 species do originate by means of natural 

 selection, but that not all species so orig- 

 inate. De Vries 's work will have a pro- 

 found and abiding influence on our evolu- 

 tion philosophies. 



II. HEREDITY: MENDEL. 



De Vries made a thorough search of the 

 literature of plant evolution. In an Ameri- 

 can publication he saw a reference to an 

 article on plant hybrids by G. Mendel, pub- 

 lished in 1865 in the proceedings of a 

 natural history society of Briinn in Austria. 

 On looking up this paper he was astonished 

 to fioid that it discussed fundamental ques- 

 tions of hybridization and heredity and that 

 it had remained practically unknown for a 

 generation. In 1900 he published an ac- 

 count of it ; and this was soon followed by 

 independent discussions by Correns, 

 Tschermak and Bateson. In May, 1900, 

 Bateson gave an abstract of Mendel's work 

 before the Royal Horticultural Society of 

 England; and later the society published 

 a translation of Mendel's original paper. 

 It is only within the present year, however, 

 that a knowledge of Mendel's work has 

 become widespread in this country. Per- 

 haps the two agencies that have been most 

 responsible for dissemination of the Men- 



