338 INTRODUCTION TO CYTOLOGY 



(Enothera exhibits other genetic pecuHarities, such as the production 

 of twin hybrids, unHke reciprocals/^ and a rarity of typical Mendelian 

 ratios. These find their explanation in the phenomena outlined above. 

 In contrast to the " superlinkage " displayed by forms with catenated 

 chromosomes, those with freely assorting pairs (Hookeri; grandiflora 

 of Davis) show ordinary linkage and typical Mendelian ratios. One 

 of the most important conclusions to be drawn from these researches is 

 that (E. Lamarckiana, which de Vries regarded as a pure species giving 

 rise to mutants by some unknown process, is a "permanent hybrid" 

 whose constancy is maintained by lethal factors and whose mutants are 

 due to occasional non-disjunction of some of the catenated chromosomes, 

 to translocations, to doubling of the chromosome number, and to dis- 

 turbances of the lethal mechanism by crossing-over. Had modern 

 cytogenetical work on (Enothera begun earlier, the mutation theory 

 would have been formulated in a very different manner. Moreover, the 

 solution of the (Enothera puzzle would not have been possible without the 

 theory of reciprocal translocation, which has now become more than a 

 theory. 



1* Lehmann (1922) describes these phenomena with the aid of diagrams. 



