SOMATIC AND REDUCTION DIVISIONS IN 

 CERTAIN SPECIES OF DROSERA 



Michael Levine 



Columbia University 

 (with plates 16-19) 



Rosenberg's work on the cytology of the so-called natural 

 hybrid Drosera obovata has raised some of the most interesting 

 points so far presented in the study of the chromosomes in hybrid- 

 ization. According to Rosenberg ('03, '04, '09) Drosera longi- 

 folia has forty chromosomes in the somatic cells, which fuse in the 

 pollen mother-cell and embryo sac mother- cell and form twenty 

 bivalent chromosomes. In Drosera rotimdifolia he finds only 

 twenty somatic chromosomes and ten bivalent chromosomes in 

 the germ cells. He reports that these chromosomes are large 

 and readily distinguishable from those in D. longifolia. In D. 

 obovata, which has been considered a natural hybrid between 

 D. longifolia and D. rotimdifolia, he finds that there are invariably 

 thirty heteromorphic chromosomes in each somatic cell, while in 

 the pollen mother-cell or embryo sac mother-cell there are ten 

 double chromosomes and ten single ones. Rosenberg claims that 

 D. obovata received twenty chromosomes from D. longifolia and 

 ten from D. rotundifolia. The pairing of the homologous parent 

 chromosomes results in the formation of two kinds, namely single 

 ones and double ones. In the heterotypic division of D. obovata 

 the ten double chromosomes separate, ten dyads going to each 

 pole. Rosenberg finds that the ten single ones are distributed 

 unevenly to the poles so that some nuclei receive as many as 

 eighteen chromosomes while others receive only twelve. Not infre- 

 quently one or more of the single chromosomes are left on the 

 spindle. In the second division the nuclei may receive from thirteen 

 to sixteen chromosomes each, while the belated chromosomes form 

 dwarf nuclei which eventually disintegrate or form dwarf pollen 

 grains. All the pollen in the hybrid is sterile. 



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