Gates, Tetraploid Mutants and Chromosome Mechanisms. |;;| 



figures published proved this to be the case. The only irregularities 

 discovered were 1) the passage of one chromosome to the wrong- 

 pole of the heterotypic spindle with about the same frequency as 

 I had previously found this to occur in 0. ruhriiicn-ix and other 

 forms; and 2) the occasional omission of a chromosome from 

 one of the daughter nuclei of the second division. My fig. 1(3 

 (plate XIII), which shows this, also shows that two of the nuclei 

 contained ten chromosomes, while a third nucleus was cut. It is 

 thus perfectly evident that my material showed remarkably few 

 irregularities during reduction. Another interesting peculiarity, 

 which Geerts (1911) first called attention to, but which is also 

 evident from certain of my figures, is the failure of certain of the 

 chromosomes to split during interkinesis. I had previously been 

 inclined to interpret this as due to the wide variation which I had 

 shown to exist in the time when the split of the homotypic chromo- 

 somes occurs. Geerts figures some of these unsplit chromosomes 

 afterwards degenerating, but it is probable that some of them were 

 in my material distributed to the homotypic daughter nuclei without 

 dividing, for I rarely found chromosomes left in the cytoplasm, 

 and never found any fragmenting, such as Geerts figures. 



It is evident from such figures as Geerts (1911) publishes, 

 that his results are in the main a confirmation of mine. The only 

 differences are 1) perhaps a closer pairing of the homologous 

 heterotypic chromosomes in the material studied by Geerts; 2) a 

 tendency for the unpaired chromosomes to fragment or be left out 

 of the daughter nuclei in the heterotypic telophase. Not a single 

 case of this kind was to be found in my material. 3) Apparently 

 greater irregularity, with fragmentation of chromosomes, in the 

 homotypic mitosis. Thus it is obvious that the full number of 

 functional chromosomes was retainecl throughout the reduction 

 divisions in my material much more frequently than in that of 

 Geerts. Whether this difference was due to the time of flowering, 

 the particular weather conditions under which the meiotic processes 

 were going on, or to some unknown difference in the hybrids, is 

 not certain. But it seems probable that the more numerous 

 irregularities in Geerts' material are to be attributed to the fact 

 that his collections were made very late in the season, when the 

 plants were nearly through blooming and the weather conditions 

 must have been much less favourable. Miss Lutz (1912, footnote 

 p. 405) states that his material was collected in September and 

 October. My material was certainly collected much earlier in the 

 summer, in the height of the flowering season. 



Miss Lutz (1912) brings forward an imposing array of hypo- 

 theses to account for the various chromosome numbers now known 

 in Oenothera, hypotheses based largely upon the observations of 



