Cytology of Antennaria. II. Parthenogenetic Species

Abstract

1. In Antennaria fallax the haploid chromosome number is 42, and meiosis in the pollen mother cells is irregular. 2. In the megaspore mother cells of male intersex flowers of A. fallax, meiosis is likewise irregular. 3. In A. parlinii the haploid chromosome number is also 42, and meiosis in the pollen mother cells is irregular, sometimes failing of completion. 4. In A. canadensis meiosis is very irregular, and is frequently a semiheterotypic division, resulting in the formation of dyads of microspores. 5. In the pistillate flowers of all the seven species studied, the embryo sac originates most often directly from an unreduced megaspore mother cell. The egg cell of such an embryo develops directly, without fertilization, into an embryo. 6. In all seven species, the megaspore mother cell occasionally undergoes a very abnormal reduction division. This division usually produces three nuclei instead of two, and the homoeotypic division following it forms a hexad or other polysporic group. 7. Evidence makes it likely that the products of this division generally degenerate. 8. In A. parlinii a peculiar type of apospory was found. 9. In A. canadensis an abnormal first embryo sac division was found. 10. The approximate diploid chromosome numbers are: A. fallax 84; A. occidentalis 75-85; A. parlinii 84; A. canadensis 83-86; A. petaloidea 75-80; A. neodioica ca. 52; A. brainerdii 42. 11. The development in the seven species is diploid parthenogenesis of the Antennaria alpina type. 12. In their irregular meiosis, the parthenogenetic species of Antennaria resemble other apomictic forms, and known hybrids. 13. Various extra-chromosomal irregularities of meiosis are discussed. 14. The species are all allopolyploids resembling those which have originated through interspecific or intergeneric crossing. 15. Some of the parthenogenetic species are morphologically intermediate between the normal species. 16. The parthenogenetic species have most likely originated from crosses between existing or extinct normal, sexually reproducing species.