i 9 o8] GATES— REDUCTION IN OENOTHERA 2$ 



Galtonia and Tradescantia, a longitudinal split appears in the thick- 

 ened thread, and the double spirem thus formed breaks transversely 

 into the reduced number of chromosome pairs. Later, in these 

 forms, a secondary union between the chromosomes is claimed to take 

 place, forming a single connected chain of chromosomes (as in Oeno- 

 thera). Sometimes a pair of chromosomes lies free by itself at this 

 time. Then by further shortening the chromosomes of Galtonia 

 again fall apart into pairs, though in Tradescantia they frequently 

 remain connected even after spindle formation. The apparent 

 similarity of the chromosome chain thus described by Miyake in 

 Galtonia to the condition in Oenothera, led the writer to make an 

 endeavor to harmonize the two accounts. But instead of this, all 

 the evidence obtained from a critical study of the stages concerned 

 shows that in Oenothera a single very thick spirem breaks transversely 

 into the sporophyte number of chromosomes. A critical examination 

 of figs. 22-28 will make it clear, I think, that we are following the 

 progressive segmentation of a single spirem, and there is no room 

 for stages between, in which a double spirem breaks into two parallel 

 series of chromosomes. Moreover, it is hardly likely that secondary 

 fusions between chromosomes would take place to such an extent as is 

 shown in figs. 23 and 24. In nuclei such as fig. 20, in which a pair of 

 chromosomes is cut off prematurely from the spirem while still in the 

 second contraction, they are invariably connected at one end and 

 rarely, if ever, at the other (though sometimes the close approximation 

 of the latter ends may give the false appearance of a ring). This 

 would not be the case if they came from separate paired threads 

 merely lying side by side, so that this connection shows them to have 

 been really successive on the spirem. From this evidence the writer 

 cannot see how anything except a distortion of the facts can lead to the 

 assumption in Oenothera of two parallel threads breaking into chro- 

 mosomes. Hence the conclusion is that the double threads appear- 

 ing in the stage represented by fig. 17 have united to form a single 

 thread, which then breaks transversely into the sporophyte number 

 of chromosomes. 



This corresponds fairly well with Strasburger's 1904 (30) account 

 of the post-synaptic stages in Galtonia, and suggests to the writer 

 that perhaps after all the earlier account may be nearer the facts, 



