三芒草屬（禾本科）之胚胎發育研究

Embryology of Aristida (Poaceae)

本文研究四種三芒草屬（Aristida）植物之胚胎發育，其種類為珠柄三芒草（A. funiculata），瓶刷三芒草（A. hystrix），多型三芒草（A. mutabilis）及剛三芒草（A. setacea）。其花藥具有四囊，花藥壁由表皮（epidermis），內皮層（endothecium），中間層及營養層（tapetum）組成。營養層屬於腺體型（glandular type），其細胞最後發育成二核到四核。內皮層於花粉粒是二細胞的階段，發育出纖維狀加厚，減數分裂後，連續的質分裂形成等二側的四分體小孢子。成熟花粉粒為單孔，具三個細胞。在瓶刷三芒草曾觀察到具有更多的細胞核。胚珠是半倒生型（hemisnatropous），具二層珠被（bitegmic）及擬厚珠心（pseudocrassicellate），但是珠柄三芒草及剛三芒草則為薄珠心型，大孢子母細胞經減數分裂後形成型或線型之四分體大孢子。四分體大孢子的合點（chalazal）是有功能的，並發育成蓼型（polygonum type）的胚囊。反足細胞（antipodals）具3到13個。胚乳之發育屬於幼壁式（nuclear type）。胚胎之發育屬於紫菀型（Asterad type）。

Embryology of Aristida funiculata, A. hystrix, A. mutabilis and A. setacea has been studied. The anthers are tetrasporangiate. The anther wall comprises of an epidermis, endothecium, middle layer and tapetum. The anther tapetum is of the Glandular type and its cells become 2-to 4-nucleate. Endothecium develops fibrous thickenings when the pollen grains are at 2-celled stage. Meiosis is normal and successive cytokinesis leads to the formation of isobilateral microspore tetrads. Pollen grains are monoporate and 3-celled at the time of shedding. Supernumerary nuclei have been observed in pollen grains of A. hystrix. The ovule is hemianatropous, bitegmic and pseudocrassinucellate. However in A. funiculata and A. setacea ovules are tenuinucellate. Meiosis in megaspore mother cell leads to the formation of either 'T'-shaped or linear tetrad of megaspores. The chalazal megaspore of the tetrad is functional and develops into Monosporic Polygonum type of embryo sac. The number of antipodals varies from 3 to 13. Endosperm development is of the Nuclear type and the embryo development conforms to the Asterad type.