1907] GATES— HYBRIDIZATION OF OENOTHERA MUTANTS 11 



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different seasons. In every count the number of chromosomes in the 

 somatic tissues has been twenty or twenty-one, though I have been as 

 yet unable to determine with certainty between these two numbers. 

 Any cytologist is acquainted with the fact that one region of a chromo- 

 some group is likely to be obscure enough, owing to close aggregation 

 of the chromosomes, to prevent absolute certainty in making a count 

 of the exact number, unless the number of chromosomes happens to 

 be a small one. The evidence already mentioned shows beyond a 

 doubt that, in the large majority of cases at least, ten chromosomes 

 enter each daughter nucleus in the heterotypic mitosis, though it may 

 be that there are occasionally eleven chromosomes in one of the 

 daughter nuclei. 



Several plants of O. lata and the pure O. Laniarckiana have been 

 examined, all having fourteen chromosomes, which makes it probable 

 that fourteen is the number found in all the pure individuals of these 

 species, and twenty or twenty-one the number found in all the indi- 

 viduals of the Lamarckiana hybrid. But it will be necessar}- to deter- 

 mine the count in several more plants of each of these races before 

 this point can be settled with certainty. 



It will be of interest to know whether the number of chromosomes 

 in the Lamarckiana hybrid remains constant in later generations, and 

 also what happens when the Lamarckiana hybrid having twenty or 

 twenty-one chromosomes is crossed with O. lata or with pure 0. 

 Lamarckiana having fourteen chromosomes. I am now growing 

 plants from crosses made in last season's cultures, which it is hoped 

 will determine these interesting points. 



THE HETEROCHROMOSOMES 



In my former paper ^ (p. 91), large rings of chromatin were dcs- 



cribed as sometimes 



rem 



mitosis 



^- t'Uia ana tne Lamarckiana hybrid small ooaies aic luunu, l..^^ 

 shaped (or hollow) but of the same size as the chromosomes, from 

 which they are otherwise indistinguishable. These may be on the 

 spindle or in the cytoplasm, as described in that paper. It was 

 believed that the smaller ring-shaped chromatic bodies were condensed 





^^om tuc larger rings 



It is possible, how- 



