September 22, 1905. J 



SCIENCE. 



371 



The fifth section is headed ' Mutations ' and 

 is, we think, the most powerful in the book. 

 The author tells in two chapters of his early 

 attempts to produce races having certain ab- 

 normalities^ — a toad-flax with peloric flowers 

 {i. e., having radial instead of bilateral sym- 

 metry) and a double daisy out of a single one. 

 He tells the story of his discovery of the 

 mutating evening primrose and the way it 

 produced new varieties and species in his 

 garden. These new forms, when self -fertil- 

 ized, reproduced themselves in a high percent- 

 age of cases. His experience with these mu- 

 tating plants led him to formulate seven laws 

 as follows : (1) New elementary species appear 

 suddenly, without intermediate steps; (2) they 

 spring laterally from the main stem (not re- 

 placing it) ; (3) they attain their full con- 

 stancy at once; (4) some of the new strains 

 are elementary species, others are to be re- 

 garded as varieties; (5) the same new species 

 are produced in a large number of individuals ; 

 (6) mutations undergo fluctuating variation, 

 but the latter is not evolution and (7) muta- 

 tions take place in nearly all directions. 



An apparent difficulty to accepting muta- 

 tions as the sole source of new species is their 

 rarity. An investigation of the literature, 

 however, convinces de Vries that there is a 

 number of records of species and varieties 

 arising by mutation and in horticulture mu- 

 tating strains play an important part. In 

 the lecture on systematic atavism the author 

 shows that many mutations are repetitions of 

 an ancestral condition that has lain latent 

 (by the author's previous definition the com- 

 ing into activity of latent characters is the 

 production of positive varieties) ; and in 

 the illuminating lecture on taxonomic anom- 

 alies he cites numerous wild species that are 

 distinguished by characteristics that appear 

 to be sports and have probably arisen per 

 saltum. 



In his lecture on periodic mutation de 

 Yries sets forth the theory that in species 

 periods of rest or stability alternate with 

 periods of mutation. If ever we can produce 

 the mutating period at will then we can hasten 

 the course of evolution. De Yries concludes 

 that, despite the long periods elapsing between 



successive mutation periods in any species the 

 theory demands less time than that of selection 

 of infinitesimal variations and so fits in better 

 with the newer conclusions of physicists who 

 are tending to shorten the probable age of the 

 earth. 



The final section of the book is devoted to, 

 ' Fluctuations.' It contains a keen argument 

 against the importance for evolution of the 

 selection of minute^ variations. After discuss- 

 ing the general laws of fluctuation as enunci- 

 ated by Quetelet and Galton (and warning 

 biologists against the use of ultra-biometric 

 methods whose biological signiflcance is un- 

 certain) de Vries states that fluctuations take 

 place in two directions only; they are either 

 plus or minios. Mutations, on the other hand, 

 are going on in ' all directions.' The cause 

 of fluctuating variability is variation in 

 nourishment. (This can hardly be true of the 

 rays of Pecten, whose number is independent 

 of size and is fixed a few hours after hatching.) 



Although new species may not be produced 

 by the selection of fluctuating characters, it 

 is recognized that such selection may be of 

 great importance in improving the quality of 

 any characteristic; particularly when the im- 

 provement can be propagated by asexual 

 methods as (in plants) by cuttings. The true 

 method for the breeder of perennials is indeed 

 to combine the preservation of sports, the 

 selection of the best variants, and hybridizing. 

 In the case of annuals it will be found that 

 improvement by selection is impossible be- 

 yond a certain point and constant attention 

 is needed to maintain any advance made. In- 

 deed, it is just this difficulty of maintaining 

 an advantage that rules out selection inside 

 the species as of importance in nature. 



The foregoing is a summary of de Yries's 

 argument. Its force is sufficiently proved by 

 the widespread acceptation it has gained and 

 by the stimulus it has already given to experi- 

 mental work. 



As to the correctness of de Yries's con- 

 clusions the future alone can give the final 

 decision— doubtless in some points of detail 

 they will have to be modified. The main 

 truth of the vast importance of mutations in 

 the origin of species can no longer be ques- 



