22 



BOTANICAL GAZETTE [July 



There are of course minor differences in these accounts, Schaffner 

 (28) stating, for example, that in Lilium tigrinum there is a splitting 

 of granules in the spirem, but the linin thread remains single. Differ- 

 ences of opinion are also expressed regarding the arrangement of the 

 loops of the spirem before segmentation, and their relation to the 

 chromosomes formed. 



These two general schemes agree that the heterotypic mitosis is 

 a reduction division separating whole somatic chromosomes, while 

 the second division is longitudinal. The essence of the distinction is 

 that the first view regards the chromosome bivalents as formed by a 

 side-by-side union of homologous chromosomes through the medium 

 of parallel threads, while the second view holds to an end-to-end 

 union. It will be seen that, omitting the points which are left undeter- 

 mined, the account in Oenothera corresponds more nearly with the 

 latter scheme than with the former, though differing in some respects 

 from both. Rosenberg (25), from a comparison of forms having 

 long and short chromosomes, has attempted to harmonize the. latter 

 view with the former. He examined List era, Tanacetum, Drosera, 

 and Arum, and found that, for example in Drosera, which has short 

 definitive chromosomes much like those of Oenothera, the spirem 

 first segmented into long twisted chromosomes lying in pairs with 

 their long axes parallel. Later, as they condensed into the short, 

 rounded definitive chromosomes, they frequently swung around end 

 to end, so that an observer seeing only the later stage would conclude 

 that they had been arranged tandem on the spirem at the time of their 

 origin. Similar conditions were sometimes observed in Listera. 

 I think my figs. 22-28 make it evident that this explanation will not 

 apply to Oenothera. The chromosomes in Oenothera do not undergo 

 any such great amount of condensation, but are already thick, heavy 

 bodies when first formed from segmentation of the spirem (fig. 24). 

 Their diameter at this time is about the same as that of the spirem 

 just previous to segmentation, as is shown by comparing figs. 22 and 

 23 with figs. 24 and 26. The fact that as many as eight or more 

 chromosomes may be found forming a single connected chain {fig. 26) 

 also renders this explanation impossible. 



Miyake (18) finds that after the pairing of elements in synapsis 

 (the exact method of this pairing need not be entered into here) in 



