“…Thus, in Anthirrhinum majus, STUBBE and PIRSCHLE (1940) and STUBBE (1953) observed that plants which were heterozygous for one or two chlorophyll-mutant genes were, in general, clearly superior in vigour to normal homozygous plants, and no indications were found that some genes had harmful effects on the heterozygote. Similarly, GUSTAFSSON (1946, 1947, 1952, 1953GUSTAFSSON et al, 1950) has demonstrated convincingly that heterozygotes for one or two of the mutant genes studied had regularly a considerably higher yield than normal homozygotes.…”