444 Allgemeine Morphologie, Pliylogeme, Deaceudenztheorie. 



Schließlich aber enthält jede Zelle verschiedene Eiweißkörper nebeneinander, so 

 daß die möglichen Kombinationen geradezu ins Unendliche wachsen. A. folgert: 

 „Es gilt ohne Zweifel das wichtige Gesetz für die ganze Organismenwelt, daß 

 jeder Zellart ein besonderer Bau zukommt. Dieser ist durch die Eigenart ein- 

 zelner Bestandteile der Zelle bedingt.V Loeser. 



1182) East,E.M. and Hayes,H.K.,A genetic analysis of the changes pro- 

 duced by selection in experiments with tobacco. In: Amer. Natural., 

 Bd. 48, Heft 1, S. 5—48, 1914. 



This is an investigation of the results of selection in "pure lines" and Gros- 

 ses, carried on from the point of view of the "pure lines" experiments of Jo- 

 hannsen. Nicotiana tabacum was used for the purpose and it was found that 

 "number of leaves" per plant was a favourable character for study. Plauts grown 

 in starved conditions in pots were greatly affected in height and size of leaves 

 but there was very little effect on the number of leaves. Hence this character 

 is considered to be largely free from environmental effect. Reciprocal crosses 

 were made between tobacco varieties which differed in average leaf number. 

 Thus "Havana" ranges from 16 to 25 leaves per plant with an average of 20 and 

 "Sumatra" from 21 to 32 leaves with an average of about 27. The F^ hybrids 

 were intermediate in this respect, the Fg showed increased variability and con- 

 tained plants which combined the leaf-size and habit of growth of "Havana" 

 Avith the leaf-number of "Sumatra". Extensive series of records of a number of 

 similar crosses are given. One case is described in which a 10-leaved plant when 

 selfed gave offspring with a mean of 18 leaves and a variability of 11,24^/^. 

 This result is interpreted as due to a real mutation or germinal change in one 

 germ cell of the mother plant. The authors state that "de Vries belle ves that the 

 mutations that he has observed always breed true" — an obvious misconception 

 of de Vries' views. It is concluded that the "Halliday" variety of tobacco was 

 derived from crosses between "Havana" and "Sumatra" and not by a mutation, 

 though it is agreed that relatively wide mutations which are not merely Men- 

 delian recombinations sometimes occur. Gates. 



1183) (julick, John, T., Isolation and selection allied in principle. In: 

 Amer. Natural., Bd. 48, S. 63—64, 1914. 



The writer contends that Isolation in itself apart from selection leads to 

 divergence. It is frequently assumed that if the environment surrounding two 

 branches of a species is the same, that natural selection will act in the same 

 way upon each brauch, and that no divergence will therefore result. The writer 

 believes that such separate branches of a species will develope different types 

 of Variation and finally different methods of using the same environment, thus 

 subjecting themselves to different forms of selection. The fact is emphasized 

 that diversity of evolution could never have arisen without continuous Isolation 

 in the sense of Suspension of interbreeding. Isolation and selection are regarded 

 as the conditions that shape the form taken by heredity and Variation. The 

 conclusion is that in a group of variable and plastic organisms divergent races 

 will be produced if for many generations the species is divided into branches 

 which are prevented from intercrossing. Gates. 



