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Three western species of the genus Habenaria willd : their relationship and crossability Fisher, Emmy H.

Abstract

Relationship and interfertility of Habenaria dilatata (lursh) Hook.,H. hyperborea (L.) R.Br, and H. saccata Greene was studied. Intraspecific and interspecific crosses were made. Chromosome counts of the three species showed 21 pairs of chromosomes in the cells, except for a small green-flowered population from Manning Park with n = 42 which was considered tetraploid and possibly of hybrid origin. These counts agree with earlier ones for the three species. Since creation of the genus Habenaria Willd» these species have been included under tribe Ophrydeae, which now has been changed to Orchideae, subtribe Orchidinae to conform with the rulings of the International Code of Botanical Nomenclature (1959)* In spite of apparently close relationships the species maintain their distinctness, even when growing sym-patrically, indicating barriers to outcrossing, or for plants growing in northerly regions, a lack of pollinators. Autogamous tendencies have therefore developed and H. dilatata and H. hyperborea are outcrossing or autogamous when the need arises. H. saccata seems to be self-sterile. Microsporogenesis in the species studied follows that of other orchids. The archesporial cell directly becomes the spore mother cell. All descendants of this cell stay together and divide together, forming a massula or pollen packet. Pollen mitosis results in the 2-nucleate pollen grain which is shed as such. The generative nucleus divides in the pollen tube, producing the 2 sperm nuclei, as the tube enters the ovary. Only the chalazal megaspore is functional. Three simultaneous divisions produce the monosporic, 8-nucleate Polygonum-type embryo sac. Fusion of the polar nuclei is the rule and takes place before fertilization. Triple fusion follows, hut the primary endosperm nucleus begins to degenerate usually before the r-ypote starts to divide. An haustorial susy ensor develops, which does not take part in the construction of the embryo proper. The mature embryo is an un differentiated body of 50-60 cells, suspended in the air-filled cavity of the reticulate testa. It takes from 3-4 weeks from pollination to saturation of the embryo. Intraspecific crosses were all successful. Interspecific crosses produced a higher percentage of seed with well developed embryos in IT. hyperborea x H. saccata crosses than in crosses between H. riil tata and either of the 2 other species. The tetraploid plants were successful both as seed and pollen parents. Regular meiosis would indicate allopolyploid origin. Artificial pollinations showed that gene flow is possible and that artificial crosses are easy to make. In nature isolating mec'r an isms must rrevent the species from losing their identity although hybridization may take place under favourable conditions. Control plants of H. dilatata and H, hyperhorea not emasculated and not protected showed a full seed set, indicating autocamy, whereas unpollinated H. sancata yielded only empty seed.

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