The Host-Parasite Method and the Distribution of Frogs

The rather wide differences in crossing-over between ears of the same plant suggest that significant differelices in crossover percentage in megasporogenesis and microsporogeniesis, uch as those reported by Emerson ancd Hutchinsoii, may be due merely to different envTiroirnmental conditions during the maturation of male and female gametes, a possibility which was suggested by those authors. Of the 33 plants in family A in which the crossover percentage for the first and second ea~r was determined, 20 gave a higher percentage inthe first ear, but the avTerage difference was less than 1 per cent. and was not statistically significant. L. J. STADLER COLLEGE OF AGRICULTURE, UNIVERSITY OF MISSOURI