Tests on a large scale were devised to determine if the multiple genes for kernel row number on the maize ear would show genetic linkage with known genes on several of the maize chromosomes. The linkage groups tested involved P (pericarp and cob), R (aleurone), Su, (endosperm), and Y (endosperm color) chromosomes.

A very significant correlation between cob (and pericarp) color and row number was discovered in a large series of crosses. This was so pronounced that one is inclined very strongly to believe that one of the major row-number genes is located on the P chromosome.

The experiments involving aleurone color (C and R factors) and row number gave some evidence of a correlation. This was particularly true when the R-aleurone factor was involved with row number. The correlation or linkage was intangible in some crosses, and yet the bulk of the data pointed to the probability that a row number gene was also to be found on the R-chromosome.

When the Su-chromosome was tested for the existence of still another row-number gene, a variable lot of data appeared. Certain crosses exhibited all the phenomena of genetic linkage between this endosperm character and row number; and yet there were enough exceptions to cast doubt on the existence of such a simple relationship as an ordinary linkage. In fact several cases of distinct reversal of linkage (parental classes occurring less frequently than non-parental) were noted, a situation which would seem to necessitate a reinvestigation of this problem.

Some evidence of a genetic linkage between the Yy endosperm color and row number was obtained. It was significantly present in the majority of the hybrid generations. The intensity of this linkage, however, must be relatively low.

In general, one may deduce from a large series of experiments such as these that the inheritance of row number is relatively complex, that the phenotype of row number is not always an indication of its true genotype even aside from environmental influence, and that the detection of genes for row number on the various chromosomes of maize is exceedingly difficult.