Microsporogenesis and Embryogenesis in Quercus

Abstract

Representative species from two subgenera in the genus Quercus were examined for floral structure and phenology, microsporogenesis, and embryogenesis. These were Quercus alba in the Lepidobalanus subgenus and Q. coccinea and Q. ilicifolia from the Erythrobalanus group. The male flowers of the three species are borne either on catkins which develop in the axils of scale leaves of the current vegetative bud or in separate male buds. Meiosis occurs in the spring at the beginning of bud enlargement; division figures were regular in all the material observed. A haploid chromosome number of 12 was confirmed for the three species. Pollen was shed on May 10, 1962, from trees of Q. coccinea and Q. ilicifolia and on May 26 from Q. alba. The female flowers are located in the axils of the new leaves. Seed development requires one growing season in Q. alba, but two growing seasons are required to mature seed of Q. coccinea and Q. ilicifolia. The chronology of embryo development is similar for Q. coccinea and Q. ilicifolia; embryo development of Q. alba is about 2 weeks behind that of the other two species. Definition of ovule dominance within a fruit occurred at the time of early embryo development. Failure of this physiological expression of dominance results in multiseeded acorns. No abnormal embryogenesis per se was observed in relation to multiple seed development.