The c-m2 allele is under the control of the Ac-Ds controlling element system. The c-m2 mutational events are most unusual (McClintock, Carnegie Yearbook 47:155-69, 1948). This allele produces mutations of at least two qualitative types (distinguished by their ability of cross-feeding the other type); within each type there is a series of mutants showing quantitative differences in pigment intensities. These quantitative differences (as observed in c/c/c-m2 seeds) range from very faint pigment (less than that produced with one dose of C) to very dark pigment (more than that produced with three doses of C). These quantitative differences were often seen as twin spots of darkly pigmented cells adjacent to pale cells (McClintock, PNAS 36:344-55, 1950). In the process of testing for c-p type expression among mutable c sources, I found that when c-n Ac x c-m2 ac or c-m2 Ac x c-n ac seeds were germinated under light sectors of light-inducible pigment became apparent. These areas of light-induced pigment were often seen as part of a twin spot with an already pigmented (c-m to C) sector.

Sheila McCormick

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