1908] GATES— REDUCTION IN OENOTHERA 13 



What significance this early separation of chromosome pairs may 

 have is not known, but it appears that the later history of these pairs 

 on the spindle can be traced. In the paper just cited (11), the 

 writer wrongly identified them with the smaller nucleoli which persist 

 by the heterotypic spindle. These chromosome pairs are frequently 

 so closely approximated at the end opposite the end of actual connec- 

 tion as to give the appearance of a ring. It was thought that these 

 rings by condensation (which actually takes place) were reduced to 

 the size of these nucleolar bodies. The latter had the size and shape 

 of chromosomes, and with a certain depth of stain invariably appeared 

 hollow. These pairs are not condensed to rings, however, but to 

 chromosome pairs of the ordinary Oenothera type. 



The spirem at this time varies greatly in thickness in different 

 parts, exhibiting constrictions and dilatations which indicate more 

 Or less clearly where segmentation into chromosomes will take place. 

 This segmentation may happen while the spirem is still in the con- 

 tracted condition {fig. 23), or after it has again uncoiled and distrib- 

 uted itself in the nuclear cavity (figs. 24, 26, 28), or before this 

 uncoiling is completed. The segmentation appears to be in some 

 cases nearly simultaneous (fig. 24) ; in other cases the segmentation is 

 successive, as in fig. 23, where the spirem is clearly divided into three 

 portions and the constrictions for the formation of the chromosomes 

 are so far advanced that the number of chromosomes to be formed 

 by each segment can already be foretold with practical certainty. 

 The segmentation at this time is into 14 chromosomes, the sporophyte 

 number. A large number of counts made at this time demonstrate 

 the absolute constancy of this number in all the individuals of O. 

 rubrinervis examined. It is possible, however, that individuals of this 

 race may be found whose chromosome number differs from this 

 number by one. This matter will be discussed later. 



In every single case where the count could be determined with 

 certainty it was shown to be 14. These counts were all made from 

 sections 10 /"• thick, and from nuclei which were uncut by the knife. 

 The less numerous counts made in the multipolar stage of the hetero- 

 typic spindle gave invariably the same number. In this case all in a 

 given cell were obtained by examining the adjacent sections. In all, 

 hundreds of counts were made. In such nuclei as figs. 26, 2p, 30, 31 



