XV] Mtitatioii 287 



preference of the one special group of facts — the merlstic — 

 as beinor in their nature more fundamental and homooeneous, 

 and my object was rather to map out the ground than to 

 erect a definite proposition upon it. The book was to have 

 been fohowed by similar collections dealing with the other 

 manifestations of variation ; but with the development which 

 genetics almost immediately underwent, it became clear that 

 the method of miscellaneous collection was no longer the 

 most direct, and that by experimental investigation of special 

 cases progress of a far more valuable order was possible. 



Views somewhat similar to those that I had formed from 

 a general survey of the facts of variation were shortly 

 afterwards published by de Vries in his famous book Die 

 M^ttationstheorie, 1 901-3. Having at command a mass of 

 evidence far larger and more coherent than mine he was 

 at last successful in bringing workers of many schools to 

 eive these sua-Qfestions a serious consideration. For the 

 first time he pointed out the clear distinction between the 

 impermanent and non-transmissible variations which he 

 speaks oidJ^fliLctuatio^is, and the permanent and transmissible 

 variations which he calls imitations. Of his proofs, the 

 most striking, to many the. most convincing, Is that provided 

 by his study of Oe^iothera, in which he witnessed the actual 

 occurrence of sudden departures from type — not one but 

 several — by which at one step In descent distinct and 

 frequently pure-breeding types were produced. Whatever 

 be the true interpretation of these particular observations, 

 they manifestly provide examples of something so like the 

 generation of new species that in any future discussion of 

 Evolution they cannot possibly be passed over. 



We may be doubtful of the validity of the superstructure 

 which de Vries has created, and yet in full agreement with 

 him in recoenlzlno- the fundamental truth, that there Is a 

 natural distinction between fluctuational variations and actual 

 genetic variations ; that the latter are those alone by which 

 permanent evolutionary change of type can be effected ; and 

 that commonly, though, as it seems to me, not always, the 

 steps by which such changes occur are so discontinuous as 

 to merit the name Mutations. 



It is at this point that Mendellan discovery aids. 

 Whereas formerly, though the fact of Discontinuity was not 



