1.The role of polyploidy in the development of seventeen species ofAlliumwas studied. It was determined that the time of occurrence of the tetraploid divisions could be correlated with the renewal of growth of the first leaf the seedling following germination.2.In section I of the genus, leaf initiation and tetraploid divisions were found to occur when the seedlings were ten to twelve millimeters long. The tetraploid divisions, however, were never very numerous.3.All the species studied belonging to section II with the exception ofA. tanguticumandA. caeruleumfollowed the same developmental pattern asA. cepareported in 1946 by Bergerand Witkus. In its developmentA. tanguticumfollows thenutanspattern of section III. The development ofA. caeruleumwas more similar to that ofA. tanguticumthan to the other species belonging to section II that were studied.4.In studying the development of species belonging to section III, it was noted that the section could be divided into two subgroups. The first subgroup would include those species with thenutanstype of development. The second subgroup on the other hand would include those species which follow the pattern of development similar toA. porrum.