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THE AMERICAN NATURALIST [Vol.LVI 



monium shows, in the metaphase of the second division 

 in the poUen-mother-eells (Fig. 1), two groups, each con- 

 sisting of 1 extra large chromosome, 4 large, 3 large me- 

 dium, and 2 small medium chromosomes, 1 small and 1 ex- 

 tra small chromosome. Thus the somatic formula is 2(L+ 



41 -_:]M-f 2m + S+ s). Toiiaploi.l |,1 u,t. Imm arisen, 

 m rare cases, Irom these dii)l()i(l D.iliiras (2). They 

 show (Fig. 2) twice as manv cliromosomcs m (-ach of the 

 size classes, and ha\e the somatic toimula 4(1^ --41 + 3M 

 -f 2m-fS-fs). Out of many crosses of tetraploid 



