No. 518] 



VARIATION 



79 



ten-rowed F x generation, so the complication need not 

 worry us at present. 



The results of the F 2 generation show a definite ten- 

 dency toward segregation and reproduction of tin* pnrent 

 types. I might add that in at least two cases I have 

 planted extracted eight-rowed ears and have immediately 

 obtained an eight-rowed race which showed only slight 

 departures from the type. Selection from those ears 

 having a high number of rows has also given races like the 

 high-rowed parent without recrossing w ith it. It is re- 

 gretted that commercial problems were on hand at the 

 time and no exact data were recorded. It can be stated 

 with confidence, however, that ears like each parent are 

 obtained in the F 2 generation, from which with care races 

 like each parent may be produced. Segregation seems to 

 be the best interpretation of the matter. 



These various items may seem disconnected and unin- 

 teresting, but they have been given to show the tangible 

 basis for the following theoretical interpretation. No 

 hard and fast conclusion is attempted, but I feel that this 

 interpretation with possibly slight modifications will be 

 found to aid the explanation of many cases where varia- 

 tion is apparently continuous. 



Suppose a basal unit to be present in the gametes of all 

 maize races, this unit to account for the production of 

 eight rows. Let additional independent interchangeable 

 units, each allelomorphic to its own absence, account for 

 each additional four rows ; and let the heterozygous condi- 

 tion of any unit represent only half of the homozygous 

 condition, or two rows. Then the gametic condition of a 

 homozygous twenty-rowed race would be %-\-AABBCC, 

 each letter actually representing two rows. When 

 crossed with an eight-rowed race, the F 2 generation will 

 show ears of from eight to twenty rows, each class being 

 represented by the number of units in the coefficients in 

 the binomial expansion where the exponent is twice the 

 number of characters, or in this case (a + b) 6 . 



The result appears to be a blend between the characters 



