THE POLYPLOID SERIES IN OSMUNDA 



successful, in which case a potential trivalent will be represented by a pair and a 

 univalent. The reason for this may partly be seen by examining pachytene. A potential 

 trivalent in the fully extended condition is shown in Fig. 20b, and it looks rather like a 



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Fig. 22. Some other stages of meiosis in diploid and polyploid Osmunda. Permanent acetocarmine. 

 X 1000. a. Diakinesis (late prophase) in the diploid showing 22 pairs resembling those of Fig. 21 

 except that the spiral is not visible, b. The end of the second meiotic division showing two of 

 the daughter nuclei each with 22 single chromosomes, after Manton (1939). c. Diakinesis in 

 triploid Osmunda showing trivalents, pairs and univalents. For explanatory diagram see Fig. 23. 

 d. Diakinesis in tetraploid Osmunda showing quadrivalents and pairs. For explanatory diagram 

 see Fig. 24. 



pair with the third chromosome wound round it. Pairing is, in fact, only possible 

 between two chromosomes at any one point, no matter how many homologues may be 

 present, and the only effect of the presence of additional potential partners is that 

 the identity of those in contact changes from time to time. Such changes of partner, 



36 



