APPLICATION OF THE QUANTITATIVE METHOD 215 



(1894). In this work he has collected a very large number of 

 instances of discontinuous variation, or variations in respect of 

 certain organs or parts, which have suddenly arisen in a com- 

 plete and perfect state, without, as a rule, the occurrence of 

 any intermediate stages. If, therefore, argues BATESON, such 

 instances of discontinuous variation undoubtedly occur, is it 

 not possible that the discontinuity of species which is so 

 striking a fact among living organisms is a consequence and 

 expression of this discontinuity of Variation ? " ^ 



In his theory of mutation HUGO DE VRIES has emphasized 

 the principle of discontinuity of species ; he promulgated the 

 view that one species arises from another by a distinct step or 

 jump (mutation; saltation). 



Many facts discovered by the MENDELIAN SCHOOL 

 seem to be inconsistent with any theory (Darwinian or Neo- 

 Lamarckian) about the origin of species based upon the principle 

 of continuous transformation. In a number of examples, indeed, 

 primordia (characteristics) are transmitted independently from 

 one another, being in turns observable or latent through succes- 

 sive generations, without intermediate forms (plasticity being 

 taken into account). 



And moreover, as far as I know, it has been hitherto im- 

 possible, by means of ARTIFICIAL SELECTION, to modify 

 a species beyond a certain limit and to obtain the gradual trans- 

 formation of a species into another one. 



The doctrine of the constancy of species, which prevailed in 

 pre-Darwinian times, can no longer be accepted. There are, 

 however, very serious reasons to adopt the principle of the 

 independence of species, which has the same significance for 

 practical purposes, although it is different from a theoretical 

 standpoint. 



Suppose that we wish to study the numerous indigenous 

 species of Ranunculus, Vicia, Veronica or GraminecB. We 

 collect specimens and try to identify them by means of the best 

 modem floras : in those books the given information is vague, 

 often hardly approximate, or even erroneous.^ Since we are 

 continually hesitating we are tempted to believe that a species 

 is really an artificial something and that all our Veronicas or 

 Vicias are simply variants of one type. One day perhaps a 

 friend may identify our specimens. We persevere ; we look at 

 the specimens rather than at the books. Observing the plants 

 under various conditions of existence, we become aware of the 

 importance of plasticity. We acquire step by step a certain 

 degree of instinct, and the result is that we become capable of 



iSee H. M. VERNON, Variation in Animals and Plants (London, 1903), 

 p. 52. See also, in the present book, p. 36, note I. 

 2 See § 145. 



