Megasporogenesis and Development of the Embryo Sac of Cypripedium parviflorum

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Abstract
Two potential megaspore nuclei enter into the formation of the embryo sac of Cypripedium parviflorum, making it bisporic, and placing it in the Scilla-type of Schnarf or the Allium-type of Maheshwari. The so-called Cypripedium-type must be abandoned: After the 4-nucleate stage of the embryo sac, the 2 micropylar nuclei divide and form a normal egg apparatus and polar nucleus; the 2 chalazal nuclei do not divide and may fuse. The mature embryo sac is either 6- or 5-nucleate. One sperm fuses with the egg and the 2d may unite with, or lie in contact with, the chalazal group of nuclei, which then contains the tetraploid number of chromosomes. The haploid number of chromosomes is 10. A classification of the work on the embryo sac of orchids is given.

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