MEGASPOROGENESIS AND GAMETOPHYTE SELECTION IN PAEONIA CALIFORNICA

Walters , James L. (U. California, Goleta.) Megasporogenesis and gametophyte selection in Paeonia californica. Amer. Jour. Bot. 49(7): 787–794. Illus. 1962.—In the ovules of Paeonia californica, a massive archesporium produces numerous (estimated at 30–40) megasporocytes, many of which complete meiosis. Several continue into gametophyte development, which is of the Polygonum type, and at the time of fertilization there are from 1 to 4 gametophytes per ovule. Rarely does more than 1 seedling per seed appear in germination. This species is characterized by extensive translocation heterozygosity, and other meiotic irregularities, in its natural populations. It shows a complete range from plants forming only pairs to those with all their chromosomes in rings at meiosis. The latter types have as high as 90% bad pollen. The course of events in the ovules is compared with the “Renner-effect” found in Oenothera. The multiple megasporocytes and subsequent events are seen as a mechanism which insures each ovule a high probability of containing a viable egg in spite of meiotic behavior which can produce 90% sterility, and thus insures high seed set in the translocation heterozygotes.