Abstract
Summary A comparative cyto-embryological study was carried out both in the fertile diploid (2n = 18) and in a sterile natural autotriploid (2n=3x=27) biotype of Cornus mas L. In the diploid individuals a quite normal meiosis occurs, functional ripe pollen grains are formed and an entbryo-sac development following the Euphorbia dulcis-type (improperly named Fritillaria-type)) is present. In the autotriploid biotype—on the contrary—a disturbed meiosis with a varying degree of chromosome pairing was observed. Generally 1–3 trivalents and 1–5 bivalents are formed at diacinesis; but some cases of asyndesis were also detected. As a consequence polycary is very frequent and the pollen grains are completely sterile. Embryo-sac development generally follows the Euphorbia dulcis-type (8,7 and 6-nucleate embryo-sac); more rarely 5-nucleate embryo-sacs of Clintonia-type and 7-nucleate embryo-sacs with three chalazal nuclei of sporic nature (Pyrethrum parthenifolium-type) are formed. Pre and post-meiotic abortion phen...
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