zd BOTANICAL GAZETTE [july 



time. Figs. 36 and 37 are merely sketches of the spindle fibers to 

 indicate their general direction. Fig. 35 is an unusual case. A cone 

 of fibers appears to have been formed on one side only of the nucleus. 

 The fibers are coming in and finding attachment to the .chromo- 

 somes. The large nucleolus is still present, as well as two smaller ones. 



The most critical stages of reduction have now been described and 

 the remaining stages will be taken up with less detail at this time, but 

 will be presented in full in a later paper. The chromosomes are at 

 first irregularly arranged on the heterotypic spindle. As already 

 seen, during spindle formation many of the chromosomes are fre- 

 quently separate and unpaired. The attraction between the chromo- 

 somes which leads to pairing is evidently weak, so that it is doubtful 

 if any pairing takes place at metaphase between chromosomes 

 which had not previously paired. On the other hand, chromosomes 

 which have once paired, no matter how early, appear to remain 

 together until their separation in the metaphase of the heterotypic 

 mitosis. Hence probably in many cases the chromosomes pass to the 

 poles of the heterotypic spindle without having previously paired with 

 each other, that is, they were merely lying loosely in the equatorial 

 region of the spindle in metaphase, so that it was largely a matter of 

 chance which pole any particular chromosome went to. This is 

 believed to be a matter of prime importance in determining the final 

 result of the reduction divisions in Oenothera, and the nature of the 

 distribution of chromatin elements which takes place. Its possible 

 significance will be pointed out in the discussion. Fig. 38 shows the 

 chromosomes just being drawn into the equatorial plate of the hetero- 

 tvpic spindle. In the examination of thousands of spindles in about 

 this stage, one usually finds the chromosomes spread out in several 

 planes along the long axis of the spindle. Of course some of these are 

 early anaphase stages in which the chromosomes have begun their 

 journey to the poles, but the condition is seldom found where the 

 chromosomes are arranged regularly in pairs on the spindle. The 

 daughter chromosomes seldom advance toward the pole in a single 

 plane, as is the case in so many forms, but are more or less irregularly 

 strung out along the spindle in their passage to the poles. This is in 

 striking contrast with their behavior in the homotypic mitosis. 



Usually in the early anaphase of the heterotypic mitosis a longi- 



