466 



Allopolyploids 



Phleum pratense is another hexaploid species that has fre- 

 quently been treated as a diploid because of regular pairing. It 

 was regarded as an allohexaploid with three genomes, which 

 Miintzing designated N, A, and B. A few "triploids" arose along 

 with ''diploids" in twin progenies and such ''triploids" (really 



Einkorn 

 A 



/ A A \ 



Vulgare 

 ABC 



Aegilops cylindrica 

 C D 



Fig. 135. Diagram showing the relationship between the einkorn, emmer, 

 and vulgare wheats with one another and with Aegilops cylindrica. Ilkis- 

 t rated also are the hybrids which would be produced between them. In 

 their haploid stages, the einkorn wheats have genome A, the emmer group 

 A and B, and the vulgare wheats A, B, and C. Aegilops cylindrica has 

 genome C in common with the vulgare wheats and also a fourth genome, 

 D. 



enneaploids) are "autotriploids." Since each chromosome is rep- 

 resented three times, a high percentage of trivalents would be 

 expected among the sixty-three chromosomes. Actually, how- 

 ever, most of the configurations are bivalents, there are some 

 univalents, and only rarely does a trivalent appear. Miintzing 

 believes that the high frequency of bivalents indicates that there 

 is considerable allopolyploidy between the A and B genomes. 

 He does not consider multivalents a good criterion for the type 

 of potyploidy and suggests that many intraspecific polyploids 

 that have been thought to be allopolyploids are really auto- 

 polyploids that do not regularly form multivalents. 



Another hexaploid that occurs in nature is Pentstemon azureus 

 subsp. angustissimus (Gray) Keck. This has a 2n chromosome 



