Gates, Tetraploicl Mutants and Chromosome Mechanisms. | j | 



the extraordinary types which appear in their offspring. These 

 chromosome numbers are being further investigated from material 

 now in hand, and it seems evident that meiotic irregularities will 

 supply the key to the cause of this extraordinary range of variation. 



N. Heribert-Nilsson (1912), along with several Mendelian 

 writers, adopts the fallacy that because a new type (mutation) varies 

 in the later generations after its first appearance, therefore the 

 original character-change was not single but compound in nature. 

 This fallacy is particularly obvious in the case of yiyus, where dis- 

 regard of the established cytological facts leads Nils son to a quite 

 abortive attempt to explain tfte origin and later behaviour of the 

 giant types. Thus he says (p. 178) ,,Einige soeben angefiihrte Tat- 

 sachen scheinen mir dafiir zu sprechen, dass die Rieseneigenschaften, 

 durch eine Kurnulation von quantitative!! Faktoren fur Grofie und 

 Form, auf verschiedenen Individuen der Stammart verteilt, aufge- 

 baut worden sind." By an hypothesis akin to Darwin's pangenesis 

 he assumes that (p. 178) ,,innerhalb der verschiedenen Teile der 

 Pflanzen Reihen von selbstandig spaltenden quantitative!! Einheiten 

 vorliegen", and that these numerous independent factors all happen 

 to meet together in a single pair of germ cells, to produce the 

 giant type 30 ). On this hypothesis, all the intermediate and aber- 

 rant types which appear in the offspring of giyas should appear 

 rather in the same family with yiyns itself, which is not the case. 

 He does mention certain forms which he considers intermediate 

 between Lamarckiana and yigas, namely his Komb. 8 (p. 129) which, 

 judging from his description, is evidently a triploid mutant. 



The application of his theory leads Nilsson into still further 

 difficulties. Thus he says (p. 180) ,,Diese Tatsachen lassen 

 sich aber durch die Annahme erklaren, dass der yigns- 

 Typus durch eine Plus-Addition von quantitative!! und 

 kumulativen Einheiten entstanden ist, welche erst in 

 verschiedenen Organen yiyus- Eigenschaften, aber nicht 

 den ^o-s-Habitus aufbauen. Wenn dann diese Plus- 

 Komplexe zufiillig z u sammentr ef f en, so entsteht die 

 Habitus veranderung, die Mutante. Der ^as-Typus ware 

 also eine extreme und zusanimengesetztePltis-Kombination 

 von Faktoren fur Grofie und Form zu betrachten 31 )." 



This assumption, which closely resembles de Vries' premutation 

 hypothesis, therefore supposes that these numerous "factors" are at 



30) This hypothesis is put forward notwithstanding his admission (p. 219 and 

 elsewhere) that in other cases one character-change can influence many organs, e. g. 

 (p. 219), ,,die Eigenschaft der Rotnervigkeit. Diese beeinflusst nicht nur die Farbe 

 der Blattnerven, soudern auch die Farbe, die Buckligkeit und die Grofte der Blatter 

 und die Lange der Friichte." 



81) Italics his. 



