226 Varietäten, Descendenz, Hybriden. 



Gates, R. R„ The mutation theory and the species con- 

 cept. (Amer. Naturalist. LI. p. 577—595. 1917.) 



The vvriter endeavours to show that in plant and animal species 

 there are two distinct types of variability, having different geogra- 

 phical relations. The one is discontinuous, independent of environ- 

 mental or functional influence, and has given rise lo many specific 

 and generic characters, notably in plants but also in higher animals. 

 The other is continuous and apparently represents the results of 

 the stress of environment on the species in its dispersal, leading to 

 the gradual differentation of local races or subspecies whose peculia- 

 rities are ultimately intensified and fixed. The latter type of speciation 

 is notably exemplified in birds and mammals, organisms in which, 

 unlike plants, the individuals can migrate from place to place and 

 so Substitute for a stress resulting from overpopulation an environ- 

 mental stress caused by a new set of climatic and physiographic 

 conditions. 



His botanical instances the writer takes from the genera Smila- 

 cina and Maianthemum, Streptopus and Krushea, Plcuystemon and 

 Platystigma. M. J. Sirks (Wageningen). 



Gregory, W. K., Genetics versus paleontology. (American 

 Naturalist. LI. p. 622-635. 1917.) 



Discussing some quotations from papers of Bäte so n and 

 Morgan, who have both uttered their scepticism about phylogenetic 

 conclusions, based upon paleontological evidences, the writer con- 

 cludes that paleontologists can show that evolutionary changes have 

 involved progressive and measurable emphases or suppressions of 

 earlier structures or of earlier proportions, and when the progressive 

 emphases are manifested as focal outgrowths, they seem like „new" 

 structures. Paleontologists, however, are not in a position to say 

 which characters would be transmitted according to the Mendelian 

 ratio , nor can they prove what were the cytological causes of the 

 evolutionary changes which they record or infer. In that direction 

 lies opportunity for consultation with the men who study enz}^mes, 

 chromosomes, heredity and Variation. The writer holds, that „pro- 

 gressive adaptation" when cleared of all implications as to the mode 

 of evolution, Stands for a historical and verifiable process; that the 

 time for developing phylogenetic conclusions and for revising 

 comparative anatomy and Classification is always now, as fast as 

 the evidence can be gathered and analyzed. 



M. J. Sirks (Wageningen). 



Hagedoorn, A. C. and A. L., New light on blending and 

 Mendelian inheritance. (Amer. Naturalist. LI. p. 189 — 192. 

 1917.) 



A reply to Castle's paper under the same heading, that dis- 

 cusses the conclusions, forthgoing from Hoshino's researches about 

 the flowering time in peas and rice. If once a contamination of 

 genes and qualitative changes in genes be atmitted, as Castle does, 

 the writers would go farther than Castle, and declare that on this 

 assumption, we need not assume a genotypic difference between 

 the parent varieties used by Hoshino at all. But the writers differ 

 from Castle in the fact that they do not believe in qualitative 

 Variation of genes. In Hoshino's paper they find nothing which 



