On the Distribution of Mutant Characters among the Chromosomes of OENOTHERA LAMARCKIANA.

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 ascertained. 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 fertilkation 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