No. 556] DEVELOPMENT IN NICOTIAN A 225 



24 chromosomes of abnormal parentage, and only one can 

 contain the factor for abnormalness and produce the ex- 

 perimental results. If more than one contained it, the 

 ratio in F 2 would be changed. For example, if it were 

 present in two chromosomes, the ratio (as suggested by 

 Emerson) 29 must be 15:1 or in this particular case 

 where the heterozygote is distinguishable, 7:8:1. We 

 might postulate its presence in all 24 chromosomes and 

 believe, as Cannon 30 did, that parental chromosomes sep - 

 arate as a phalanx in the F x reduction division, each group 

 going to one pole and thereby bringing about the forma- 

 tion of pure parental gametes. But the cytological in- 

 vestigations of Sutton, Eosenberg, Strasburger and 

 others have brought to light evidence which precludes 

 such a supposition. The experimental data from genetic 

 researches are also opposed to this hypothesis, if one at- 

 tempts to show a relation between the reduction division 

 and Mendelian segregation. On a chromosome hypoth- 

 esis, then, one must believe the factor for abnormalness 

 to be present in only one chromosome out of the 48 con- 

 cerned in the Fj reduction phenomena, in order to be in 

 agreement with the experimental results. This being 

 the case, how is one to account for the abnormalities 

 which occur during the reduction divisions in the anthers 

 of the F x heterozygote? For they affect, not alone one 

 chromosome, but all the nuclear and cell material con- 

 cerned in the formation of the pollen grains. Can one 

 postulate the influence of one chromosome to be so great, 

 at times, as to bring destruction to its 23 associates of ab- 

 normal parentage, its 24 associates of normal parentage, 

 as well as all the other organized contents of the mother- 

 cell? Why, it may well be asked, if this destruction is the 

 result of the activity of one chromosome does not it take 

 Place in the case of every anther and of every pollen 

 mother-cell? Why should it affect only two or three 



" Emerson, R. A., « < Genetic Correlation and Spurious Allelomorphism in 

 Maize," 24th Ann. Rpt. Nebr. Agr. Exp. Sta., pp. 59-90, 1911. 



-Cannon, W. A., "A Cytological Basis for the Mendelian Laws," Bull 

 T orr. Bot. Club, 29: 657-661, 1902. 



