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THE AMERICAN NATURALIST [Vol. LIII 



cases of gametic coupling had just been published by 

 Bateson and Punnett and the subject of linkage was not 

 well understood nor its true significance realized. These 

 writers considered the possibility of gametic coupling as 

 a disturbing factor, but came to the conclusion that this 

 phenomenon could not be concerned in their aberrant 

 results. 



One of the crosses studied involved two aleurone fac- 

 tors, the basic color factor C and the factor P (Emerson's 

 Pr factor), with R present coming from both parents. 

 This cross was expected to give a ratio of 9 purples : 3 red : 

 4 non-colored, but actually showed a large excess of pur- 

 ples and deficiency of reds. East and Hayes considered 

 the possibility- of linkage between the P and R factors, 

 but since R, according to their theory, was homozygous, 

 crossing-over between these two factors would make no 

 visible difference in the results. On the other hand, 

 since PC entered the cross from one side and pc from the 

 other, the cross-over class pC, if there is linkage, would 

 be red because of the presence of R. Hence any possibil- 

 ity of linkage should be looked for between the P and G 

 factors. Such a situation would account for an excess of 

 purples and a deficiency of reds in the cross under con- 

 sideration. Another cross involving, in addition to the P 

 and C factors, a color inhibiting factor likewise showed 

 an excess of purples and a deficiency of reds. 



Since it is always rather difficult to prove linkage from 

 F2 distributions alone, in this case it would be even more 

 difficult because only one of the cross^over classes, if such 

 it is, can be distinguished. The data of East and Hayes, 

 as far as numbers go, do not agree with expectation from 

 linkage with any amount of crossing-over, and since other 

 crosses involving the same factors have been reported 

 which seem to show independence, it is doubtful whether 

 or not linkage really exists in respect to these two factors. 

 It is more probable that the deviations from theory are to 

 be looked for in either incomplete analysis of the factor 

 relations or faulty classification of the seeds. R«d seeds 



