No. 636] 



GENETIC SEGREGATION 



9 



In view of the chromosome theory of Hnkage, it is 

 therefore worth remarking that we do not find linkage 

 especially frequent among these fractional factors. 

 Have they, then, been distributed among different chro- 

 mosomes? If in Antirrhimim, the color of the face and 

 of the throat were lately parts of a-single factor for the 

 total flower-color, would not linkage betw^een them be ex- 

 pected? Nevertheless, in cases of this sort, so far as I 

 know, linkages have not been found with any special 

 frequency. 



The segregation of a group of differences — and pre- 

 sumably factors — in combination has lately been shown 

 by Renner^ to occur with extraordinary frequency in the 

 CEnotheras, and this peculiarity is without doubt at the 

 bottom of the difficulties which have beset the genetic 

 analysis of these plants. The complexes are in several 

 forms or species not borne equally by the two sexes of 

 the same plant, and most of them are unable to exist in 

 the homozygous state. These discoveries greatly eluci- 

 date the (Enothera problem. For instance, not only CEn. 

 lamarckiana, but biennis, muricata, and others also, are 

 not homozygous types, but heterozygotes of a special 

 kind. Consequently, the production by them of ''mu- 

 tants" is not capable of the simple interpretation 

 originally applied to them by de Vries. Eenner sug- 

 gests that the mutants arise owing to some interchange 

 between the complexes which at present we can not in- 

 vestigate, but whatever be the exact manner of their 

 origin we can not regard them as genuine examples- of 

 the production of novel forms by a homozygous type. 



Before leaving this part of the subject, we may notice 

 that the supposition that segregation is concerned solely 

 with characters of a superficial or trivial nature lias l)een 

 long ago disproved. Baur's Antirrhiniuii.-. tlif -tndy of 

 which was continued by Lotsy, were an excellent denion- 

 sti'ation to the contrary, for they provided many illustra- 

 tions of x'uroaation in features, the "specific value" of 

 which no >ystciuati>t WiUild question. If further evi- 



