Embryo-sac formation in diploid and polyploid species of roseæ

Abstract

During the past ten years, the author has been carrying out cytogenetical experiments with the numerous species of the Tribe Roseæ of the Family Rosacese. In the course of this research, 691 varieties have been examined eytologically and taxonomically, including representatives of 198 Linnean species and many natural and genetical hybrids of the six genera of the Tribe. Several workers have investigated the processes of pollen formation and male gametogenesis, but, owing to various technical difficulties, no one has yet published a consecutive and comprehensive account of the processes of embryo-sac formation in the species of this Tribe. Hoffmeister (1858) and Strasburger (1878) examined a few species of Rosa and found that several embryo-sacs were formed in one ovule. Péchoutre (1902) discovered two fully-developed embryo-sacs in one ovule in one species of Rosa , and both he and Strasburger found that the micropylar cell of the quartet develops to form the embryo-sac. Tackholm (1920, 1922) examined the formation of embryo-sac mother cells in the irregular polyploid Species of the Caninæ Section of the genus Rosa , and discovered the remarkable unequal reduction division th at takes place in the embryo-sac mother cells of these species, but technical difficulties in sectioning the older ovules and achenes prevented an investigation of the later stages. It seems desirable, therefore, to publish a general account of the processes of embryo-sac formation in Roseæ, since the research covers new ground.