THE REDUCTION OF THE CHROMOSOMES 



253 



mitosis, each microspore (after the second mitosis) having as a result 

 three chromosomes: one long, one medium sized, and one short. Since 

 the gamete receives such a simplex group of three chromosomes, and the 



Fio. 100. Heterotypic mitosis in Triticum potonicum X T. spelta. 

 A, the 21 chromosomes (polar view). B, 14 bivalents separated into component 

 univalents; 7 unpaired spelta chromosomes have split and are about to be distributed. 

 (After Kihara, 1919.) 



somatic cells of the new individual show six (two of each length), it is 

 evident that the other gamete furnishes a similar simplex group of three. 



FIG. 101. The chromosome complement in the spermatocyte of Brachystola 

 magna. (After Sutton, 1902.) 



In Najas marina and Najas major (Miiller 1911; Tschernoyarow 

 1914) the duplex group of 14 chromosomes is made up of seven visibly 

 different pairs (Fig. 56 bis). In the heterotypic prophase these conjugate 

 selectively to form seven bivalents, the reduced nuclei therefore receiving 



