In MacArthur's 1929 X-ray experiments with Earliana seed the mutant 263M was characterised by extremely slow growth and smaller cotyledons and leaves. After being selfed for several generations and selected for vigour the plant lost its slow-growing character and only retained the narrow cotyledons. Plants with this character have been crossed with a number of different P1's and the F1 is perfectly normal while the F2 gives good 3 to 1 ratios. A typical ratio for a repultion cross with lutescent being Nc L 547 : Nc l 226 : nc L 191 : nc l 75 which gives a monohybrid Chi-square of 0.2 for narrow cotyledon.
A typical plant has cotyledons of normal length but only half as wide as normal. Since cotyledon size varies with the age and ancestry of the seed no single set of measurements would satisfactorily characterize nc, but it can be classified with certainty except in F2's segregating for dwarf. The thick broad cotyledons of dwarf plants are not as strongly modified and some d\1\nc plants are apt to be classified as Nc.