256 



THE AMETtlCAX XATmALIST [Vol. LV 



Somatic Number of ('hkomosomes and rKi;< i:NTA<;K, of Bad Pollen 

 FoL-ND IX Normals and in Diffk.rknt iEuTAXTS 



transmit it tlirougli the egg cells, although to only about 

 one quarter of the offspring. That the offspring of these 

 mutants repeat the parental type regularly in less than 

 the 50 per cent, expected is probably due to the lessened 

 vigor of growth of mutants in comparison with normals. 



If the presence of an extra chromosome in a given set 

 causes a specific mutation due to the constitution of this 

 particular chromosome, rather than to the mere pres- 

 ence of an extra chrom'osome irrespective of its origin, 

 there are at least two consequences to be expected. First 

 there should be as many possible mutants of this type as 

 there are chromosome sets which may undergo duplica- 

 tion. In other words there should be 12. Twelve, as a 

 matter of fact, is the actual number which we had found 

 before the nuclear condition had been determined. In 

 addition, we have two or three mutant forms apparently 

 belonging to this class for which it has no^t yet been pos- 

 sible to obtain chromosome counts. In appearance they 

 are combinations or modifications of members of the 



