802 



SCIENCE 



[N. S. Vol. XXVIII. No. 727 



existence and selection; de Vries's mutation 

 theory ; a new section on " Heredity " (in 

 former editions omitted, singularly enough, as 

 a presupposition of selection) ; an extensive 

 enlargement of the section on variation, and 

 a thorough revision of the final chapter — " the 

 applicability and limitations of the Darwinian 

 and Lamarckian factors." Through these ad- 

 ditions the book has been doubled in size and 

 value. 



The greatest interest naturally attaches to 

 the author's position on the newer questions 

 of the day relating to mutation and heredity — 

 questions that were merely shaping themselves 

 at the time the second edition was written, 

 four or five years ago. In regard to the theory 

 of saltation, which is considered historically 

 in a thorough fashion, the author concludes 

 that, on account of their rarity and their 

 prevailingly pathological character, saltations 

 have only the significance of exceptional phe- 

 nomena not properly to be considered as play- 

 ing the part of making variations that are, 

 on account of their size, directly of selectional 

 value. 



As for the mutation theory, which the 

 author treats quite separately from saltation, 

 he concludes — after a valuable summary of 

 de Vries's work — that it is a modified theory 

 of selection from which the idea of the in- 

 heritance of somatic variations has been 

 eliminated. At the outset Plate calls atten- 

 tion to the fact that de Vries has not only 

 applied the name mutation in a new (and ill- 

 defined) sense, but has used the term " fluc- 

 tuating variability " in an opposite sense from 

 Darwin; since for Darwin' fluctuating vari- 

 ability is the ordinary inheritable variability 

 as opposed to " definite variability " resulting 

 from direct action of changed conditions and 

 commonly regarded as non-inheritable; while 

 for de Vries fluctuations are due to varia- 

 tions in nutrition and so faU into Darwin's 

 category of " definite variations." Using for 

 the present de Vries's terminology, the type 

 of mutation is that of (Enoihera lamarckiana, 

 in which a number of characters change 



^ " Variation of Animals and Plants under 

 Domestication," chapter XXVI., summary. 



simultaneously to produce each of the mutants. 

 Unfortunately this type case is an exotic in 

 Amsterdam, where its mutability was first 

 discovered, is unknown in the wild state and 

 is very probably a hybrid. In any case the 

 proportion of mutants produced is small, they 

 lack adaptive features, and, in general, muta- 

 tion is a rare phenomenon. In consequence of 

 all these reasons mutations can play little 

 part in nature. Plate opposes the extension 

 of the term mutation to cover saltations and 

 fluctuations in Darwin's sense (the ordinary 

 variation of single characters), and so leaves 

 it reduced to its lowest limits and shorn of 

 any great significance. This treatment strikes 

 the reviewer as not altogether just. De Vries's 

 theory deserves more credit at least for this 

 that it stemmed the tide of exclusive atten- 

 tion to quantitative variation that was threat- 

 ening to obliterate the study of the origin and 

 inheritance of new characters ; i. e., variations 

 of the qualitative order ; it stimulated a study 

 of the origin and inheritance of variations by 

 the method of experiment. 



The section on heredity contains two prin- 

 cipal parts: The first deals with the inherit- 

 ance of acquired characters, the second with 

 Mendelism. As for the first the author accepts 

 as demonstrated the inheritance of the effects 

 of heat, light, etc., on insects, fishes and 

 plants; he lays stress on the difference of 

 pigmentation on the two sides of the flounder 

 — a difference which, while associated with the 

 different exposure to light of the two sides 

 of the body in the adult, begins to appear 

 before the young fish abandons its vertical 

 attitude in the water. He regards as critical 

 Semon's investigations upon the seedlings of 

 sensitive plants which, without having ex- 

 perienced the alternation of daylight and 

 darkness, nevertheless show an innate tendency 

 to open their leaves for twelve hours and shut 

 them (for sleep) during the alternate twelve 

 hours. He cites the loss of pigmentation of 

 cave animals as evidence of the transmission 

 of a somatic character to the germ plasm, but 

 fails (the reviewer believes) sufficiently to ap- 

 preciate the evidence for an orthogenetic 

 tendency in these cases toward loss of pigment. 



