There are two independent factors,N1 andN2, which are normally present in the Kale type ofB. oleracea; when both these factors are absent, the common Cabbage heart developes under normal cultural conditions. Intermediate degrees of “hearting” are produced by one or two “doses” ofN.
The Heart character shows “linkage” with a number of other characters. Clearly it is of interest to determine, in each case, whether linkage is with the factorN1 or withN2.
There is one linkage group comprising the factorsN1, P for petiolate leaves as against sessile,E for entire leaves as against lyrate, andW which determines broad as distinct from narrow leaves. There is some evidence that there is also in this group a factorK1, one of the multiple factors for the Curly foliage of Scotch Kale.
There is a second linkage group containing the factorsN2,T for tall habit as against sessile habit, and probably the factor K2 of the curly series.
There are two so far unattached factors, one of which,D, differentiates between the purple and green types ofoleracea; the other,A, determines the “Asparagodes” malformation of the foliage.
Thus the ten factors so far considered account for four of the nine chromosomes ofB. oleracea.
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