686 



SCIENCE. 



[N. S. Vol. XXIII. No. 592. 



included the chapters treating of de Vries's 

 work on the production of the peloric toad 

 flax, double flowers and new species and 

 varieties of CEnothera. He also presents 

 his views, with his seven laws, on 'the 

 origin of wild species and varieties.' The 

 last four chapters are entitled Mutations 

 in Horticulture, Systematic Atavism, Tax- 

 onomic Anomalies and Periodic Mutations. 

 Interesting data are presented in each one 

 of these chapters. The phenomena of 

 mutation in horticulture and taxonomic 

 anomalies are in general in line with the 

 general thesis being defended. 



The idea that the species are constant 

 through extended periods of time, follow- 

 ing which is a period of mutation with the 

 production of new forms, those best ac- 

 commodated to the environment surviving, 

 is important. 



Dall proposed the term saltatory evolu- 

 tion in 1877, and suggested periodic muta- 

 tion. His conclusions, however, did not 

 rest on observed experiments. 



VI. The last section of the book deals 

 with ' fluctuations. ' An account is given of 

 the means of the statistical study of varia- 

 tion. Quetelet's law is stated, etc. In 

 this section it is contended that fluctuating 

 variation does not exceed certain definite 

 limits, and that in cultivation, without the 

 appearance of desirable mutations, it is not 

 possible to ameliorate a species beyond a 

 fixed degree. Ameliorated races, without 

 continual selection, regress toward the mean 

 of the species. In the last chapter of the 

 book it is maintained that natural selection 

 can do no more toward the creation of new 

 species by an accumulation of fluctuating 

 variation than can artificial selection. 



From this very defective review of de 

 Vries's work, it will be seen that he has 

 investigated a wide range of phenomena. 

 His method has mostly been by experi- 

 ment; his results are such as to compel a 

 critical reexamination of the views current 



on the process of evolution. I shall hastily 

 criticize the three theories stated in the 

 beginning of this discussion. 



1. The Darwinian Hypothesis. — Accord- 

 ing to researches into the variability of 

 organisms, fluctuating variation is around 

 a mean and never transgresses certain 

 limits. It is not possible to ameliorate a 

 particular species beyond a flxed degree, 

 and it is, therefore, impossible radically to 

 change it. If continued artificial selection 

 is not practised, the ameliorated race re- 

 gresses toward the mean of the species. It 

 is contended by de Vries that the same is 

 as true of wild species as of those in cul- 

 tivation. If the criticism can be sustained, 

 this hypothesis must be abandoned. 



2. The Dynamical Hypothesis. — Dall, in 

 his paper entitled 'On Dynamic Influences 

 in Evolution,' said: 



Passing from these general considerations to 

 those of a more special character, the contention 

 of Weismann that ' not a single fact hitherto 

 brought forward can be accepted as proof ' of the 

 transmission of acquired characters demands at- 

 tention. 



In reply he says : 



If the dynamic evolutionist brings forward an 

 hypothesis which explains the facts of nature 

 without violence to sound reasoning, that hypoth- 

 esis is entitled to respect and consideration until 

 some better one is proposed or some vitiating 

 error detected. 



Some years ago, while a student at Har- 

 vard, I had the opportunity to attend a 

 symposium on the hereditary transmission 

 of acquired characters. The principals in 

 the discussion were Professor Poulton, of 

 Oxford, and Professor Alpheus Hyatt. 

 The data presented by Professor Hyatt 

 were subsequently published in his memoir 

 entitled 'The Phylogeny of an Acquired 

 Characteristic' After the discussion, my 

 conclusion was that Professor Poulton had 

 shown that all experimental evidence was 

 against the transmission of acquired char- 

 acteristics; while Professor Hyatt pro- 



