DOUBLED CHROMOSOMES OF OENOTHERA 

 LAMARCKIANA SEMIGIGAS. 



WITH K. BOEDIJN 



Introduction 



In a previous paper (8) we have tried to show that the numerous 

 types of the mutants of Oenothera Lamarckiana may be combined 

 into groups. We started from two principles: the frequently repeated 

 production of one type by another, and the striking external resem- 

 blance of forms which were different in their hereditary features. 

 0. mut. albida is produced almost yearly by 0. mut. lata, and in a 

 relatively high percentage. 0. mut. oblonga almost always is seen 

 in large numbers among the progeny of 0. scintillans. It is evident 

 that such repeated productions point to some kind of intimate 

 connection, such as can be explained only on the assumption that 

 the factors for the two types are located in the same chromosome. 

 On the other hand, in all its organs 0. mut. nitens shows the same 

 characters as 0. mut. scintillans, although the first type is constant 

 whereas the other splits, in each generation, into specimens of its 

 own form and others of the type of 0. Lamarckiana. The external 

 features being the same for both, their factors must also be assumed 

 to be the same, at least mainly. 0. mut. nitens and 0. mut. scintillans y 

 therefore, were assumed to be located in the same chromosome. 



Applying these principles to the great majority of the mutants, 

 we had seven groups, corresponding to the seven chromosomes of 

 the haploid nucleus. One of them consisted chiefly of the isogamic 

 mutants, but in each of the others one of the dimophic or splitting 

 mutants prevailed. Accordingly we proposed to call the chromo- 

 somes after these. The name of central chromosome was chosen 

 for the one containing mainly isogamic types, and two of the others 

 were called after 0. mut. lata and 0. mut. scintillans, reserving the 

 names of carta, pallescens, liquida, and spathulata for the four remaining 

 ones. The three first groups were found to be large; they may cor- 

 respond to the three large chromosomes described and figured by 

 Cleland for 0. franciscana (2). The four other groups would then 

 correspond to the four smaller chromosomes of the haploid nucleus. 



