164 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



SPECIES AND VARIETIES: THEIR ORIGIN BY 

 MUTATION. 



A Criticism of De Vries. 



By Rev. Prof. G. Hexslow, M.A., V.M.H., &c. 



After studying De Vries' work with the above title, the question that 

 arises in one's mind is : Has he discovered anythiug new, or is he only 

 giving a new name to a well-known fact ? 



The essence of Mutation lies in the sudden and spontaneous ap- 

 pearance of a "forni" with several small deviations in morphological 

 characters from the parent species, which are constant when tested by 

 heredity. 



If variations be not constant, then they form " fluctuating varieties." 



Darwin's theory, however, also requires constancy, or a new species 

 could never have arisen at all. Thus he says : " Any variation which 

 is not inherited is unimportant to us ; but the number and diversity 

 of inheritable deviations of structure, both those of slight and those 

 of considerable physiological importance, are endless."* "Perhaps the 

 correct way of viewing the whole subject would be to look at the 

 inheritance of every character whatever as the rule, and non-inheritance 

 as the anomaly." t So too M. Carriere said : " Tout tend a se repro- 

 duce et meme a s'etendre, que par consequent les modifications peuvent 

 non-seulement devenir hereditaires, mais qu'elles peuvent encore servir de 

 moyen pour arriver a d'autres modifications." i Again, " Tout individu a 

 une tendance a reproduire ses caracteres." § 



Indeed, if the variation were not constant from its first appearance and 

 receive successive increments as Darwin supposed, how could the new 

 variety or species come into existence at all ? Similarly, if we follow the 

 views of Neo-Lamarckians, and regard new variations which arise through 

 the direct action of changed conditions of life not to be constant, no 

 new form would be stable or any permanent adaptation exist as seen in 

 every living being. This is the view of Warming, Costantin, and other 

 Ecologists, as well as Darwin himself, in his alternative view to natural 

 selection. Let us now get a clear idea of this new conception of species. 

 We all know what is meant by a Linnean species, which is, at least 

 theoretically, based on two categories : (1) a collection of morphological 

 characters of sufficient importance to differentiate it horn all other species 

 of the same genus ; (2) a presumable if not provable hereditary 

 constancy. 



De Vries, however, regards a species not as an entity, but an aggre- 

 gation of "real units " or " elementary species," just as a " genus " is an 

 aggregate of "species." "Any form which remains constant and distinct 



* Origin of Species, etc. 6th ed. p. 9. f Op. cit., p. 11. 



X Production et Fixation des VariCte's, 1865, p. 9. § Ibid. p. 17. 



