1907I GATES— HYBRIDIZATION OF OENOTHERA MUTANTS 



19 





mes usually become t 

 3 arises from the pear 

 ^ not been determined 



Just 



mitosis 



chromosomes are nearly always two-Iobed or dumb-bell-shaped and 

 can be readily counted (seven in O. Lamarckiana) in this condition. 

 They soon become more or less irregular in outhne, however, as the 

 nuclei pass into the resting condition, but this characteristic shape 



time 



membrane 



Several interesting features have appeared in connection with the 

 examination of nuclear divisions, in various somatic tissues, a work 



t com 



time "^ 



All the tissues examined 



mother 



observed 



examined 



lata^ O. Lamarckiana^ and the Lamarckiana hybrid), except for the 



number 



In the tissue of the anther 



wall and in the rapidly dividing tissues of the young petals, in both of 

 which a great many chromosome counts were made, the chromo- 

 somes are crescents, rods, or loops in metaphase and the early ana 

 phases, the apices of the loops converging in telophase to the poles 

 of the spindle. In the telophase these chromosomes also become 

 two-lobed or dumb-bell-shaped. This shape is 



ery 



and 



constant, or at least occurs very 



at this 



stage. Observations which 



chromosomes 



This 



very 



formed 



chromosomes can 



counted at this time, and the number is apparently constant in each 

 form. It seems probable that this clubbing of the ends of the chromo- 

 somes to form dumb-bells or two-lobcd chromosomes in the telophase 



tens 



telophase of the heterotvpic mitosis, giving rise to the tetrad appear 



ance 



. and in the telophase of the homotyp 

 lobed or dumb bell-shaped chromosomes. 



Whether 



appearance is m all these cases 

 mitosis cannot at present be dctc 



