The genetics of cotton. Part II. The inheritance of pollen colour in New World cottons.

1. A single genetic difference is involved in all crosses between any grade of yellow and grade 0. That is, yellow and pale cream form a simple pair of factors, which may be denoted as P and p. 2. Modifying genes act on the basal gene for yellow, producing a complex series of shades from pale yellow 0.5 to deep golden 4.0. These modifying genes can be carried by grade 0, producing such minute variations in shade as are exemplified by Superokra and G.W.P. 3. P produces little effect when unsupported by modifiers, and the distinction between P and p is often hard to make in Segregating families lacking such modifiers. It is possible that in the absence of any modifier at nil, the distinction between P and p would vanish, i.e. P would produce too pale a shade of yellow to observe segregation. 4. In crosses between cottons of the same class, e.g. inter-Peruvian or inter-Upland, segregation is usually very sharp, owing to similar modifying factors being present in a homozygous condition in both parents. 5. In the selfed back-cross (Upland • Sea Island) • Sea Island, an intensifier, Q, was demonstrated, having no visible effect except in presence of P.