ON THE DISTRIBUTION OF MUTANT CHARACTERS 



AMONG THE CHROMOSOMES OF OENOTHERA 



LAMARCKIANA. 



WITH K. BOEDIJN. 



During the last ten years the number of distinct mutant types of 

 Oenothera Lamarckiana has increased considerably. One of us has 

 determined the chromosome numbers for most of them, including 

 those older ones, for which these figures had not as yet been ascer- 

 tained. Moreover the fact that some mutant types are repeatedly 

 produced by others has become very prominent, indicating some 

 kind of genetic relationship. Outward features are often observed 

 to run parallel with such connections; in other cases they are so 

 much alike, as to give another trustworthy basis for the assumption 

 of closer relations. 



Starting from these facts, we have tried to arrange the mutant 

 types into distinct groups, analogous to those proposed by Morgan 

 and his disciples for Drosophila. Unfortunately, it is in our case 

 mostly impossible to determine dihybrid splitting figures, such as 

 constitute the basis for Morgan's deductions. Differences in the ratio 

 of growth of the pollen tubes, preferential fertilization of one of the 

 kinds of egg-cells, in those cases where there are two or more of them, 

 deviations in the partial sterility of pollen-grains and of seeds are 

 among the main causes which tend to discard numerical data from 

 our present considerations. But the distinctness of our results does 

 not seem to suffer from this difficulty. We start from the numbers 

 of the chromosomes, and bring those mutants, which do not deviate 

 in this respect from the main species, into our first group. In doing 

 so, we find that almost all of them belong to the ordinary types of 

 mutations. They are mostly due to recessive characters, as, for 

 instance, the dwarfs and the brittle races. 



In a large number of the other mutants one of the chromosomes is 

 doubled, bringing the total number of these bodies up from seven 

 to eight in the haploid cells, and from fourteen to fifteen in the 

 somatic nuclei. Here, however, it is clear that the relations are not 

 so intimate as to allow the combining of all these forms into one 



