THE BREEDING GROUP AND SEED STORAGE: A STUDY IN POPULATION DYNAMICS

This is a report on the yearly frequencies since 1941 of blue and white flowered plants of Linanthus parryae, a conspicuous annual of the Mojave desert. Like most desert annuals, its abundance and dispersion varies greatly from year to year and from place to place in response to weather. The size of the breeding group would be expected to vary with these expansions and contractions. An initial survey (Epling and Dobzhansky, 1942) suggested that the inheritance of color depends on one pair of alleles. Having these natural markers, the species appeared to be a useful subject with which to study the effects of selection and genetic drift. The initial survey sampled a naturally delimited area of about 600 square miles. Linanthus was extraordinarily abundant in 1941 and the population was almost literally continuous throughout the area (fig. 1) . For the most part it consisted of white flowered plants. Three mixed areas were found, however, in which the color frequencies were locally highly variable. Only occasional blue individuals or small patches were observed in some parts of the white area. Subsequent sampling has shown that these mixed areas are persistent and that their limits have not materially changed. Four years sampling of the westernmost mixed area by the coarse method used in the initial survey also indicated that color frequencies tended to remain constant in very local populations. Permanently marked experimental plots were accordingly constructed within this area, which have permitted a systematic and detailed sampling of dispersion and flower color each year since 1944. The exact mode of inheritance of flower