1907] GATES— HYBRIDIZATION OF OENOTHERA MUTANTS 15 



remain 



out in the cytoplasm. Rosenberg'^ found 

 such a situation in the Drosera hybrid, where the ten chromosomes 

 from one parent paired with ten of the twenty from the other parent, 

 while the remaining ten chromosomes of the latter remained unpaired 

 and were irregularly distributed or lost in the cytoplasm. But nothing 

 of this kind has thus far been observed in the reduction divisions of 

 the Lamarckiana hybrid, and instead ten chromosomes are apparently 

 regularly distributed to each daughter nucleus in the heterotypic 

 mitosis. It is pretty evident that the exact number of chromosomes 

 cannot be satisfactorily settled until their origin is ascertained. 



Not the least remarkable part of this situation is found in the fact 

 that here we have two plants, the pure O. Lamarckiana and the 

 Lamarckiana hybrid, which cannot be distinguished by their external 

 characters, and yet differ widely in the number of their chromo- 

 somes. This difference in number assumes a different aspect, how- 

 ever, if we find, as seems most probable, that we have here merely an 

 extra set of chromosomes from one parent. Such a situation need not 

 necessarily interfere with the present views of persistency of chromo- 

 some numbers or even of the ordinary' constancy in number for a 

 species. A knowledge of the fate of these chromosomes in subse- 



ermmi 



the general bearing of these facts on present views of the individuality 



and constancy in number of chromosomes. 



It is suggestive that in the Lamarckiana hybrid, as Rosenberg' °' 

 has found in the apogamous species of Hieracium, the number of 

 chromosomes is much higher than in other species of the genus 

 examined. In the apogamous species in various genera investigated 

 in recent years, where the chromosome numbers arc known, the 

 number of chromosomes in apogamous species is nearly or exactly 

 double the sporophyte number in closely related, normally fertilized 

 members of the same genus. A list of these cases need not be given. 

 There may be a suggestion here as to how variation in the chromo- 

 some numbers of a genus originates. The same author'" finds that 



'* Rosenberg, O., Ueber die Tetradentheilung eines Drosera-Bastardes. Ber. 

 I^eutsch. Bot. Gesells. 22:47-53. Pl- 4- i9°4- 



'« Rosenberg, O., Cytological investigations in plant hybrirls. Rep. 3d Internal. 

 Conf. on Genetics. Jour. Roy. Hort. Soc. London 24:289-291. 1906. 



