473 



thé division, in the heterotypic anaphase, of one of Ihe unpaired 

 cliromosomes. Probably both unpaired chromosomes somelimes 

 divide although no P. M. C. have been seen with ten chromosomes 





;■ // 



i! / 



%^ • 



9X 



d 



V\g. 1. a and b Nicotiana ulata, homot3'pic anaphases. 

 a, two plates containlng 8 and two containing 10 

 chromosomes. c and d Nicotiana Tabaciim var. "Mira- 

 dato" X N. syloestris, Fj. c, heterotypic metaphase in 

 E. M. C, polar vievv, 12 bivalents and 12 univalents. 

 d^ and d^, heterotypic anaphase in P. M. C, 11 bivalent 

 partners at each pole and 1 undergoing separation, 11 

 single chromosomes dividing and 1 undlvided 

 in the equatorial region. 



in all fonr anaphase plates. In view of these rcsults further study 

 of this somewhat polymorphic species is necessary. Most commonly 

 all foiir anaphase plates contain nine chromosomes and undoubt- 



