Cercidiphyllum Branch (cercidiphyllaceae,) Embryology Department Is A Comparative Study

The eastern endemic families:Cercidiphyllaceae and its related families:Eupteleaceae and Trochodendraceae share great importance in the research of angiosperm systematic evolution.We perform investigations by using the technologies of paraffin sections and hemi-thin slices,including microsporogenesis,megasporogenesis,male and female gametogenesis of Cercidiphyllaceae,and also do some embryological research of Eupteleaceae and Trochodendraceae in addition,to discuss the Cercidiphyllaceae's systematic position based on comparing the embryological characters with their related families.The main results are as follows:1.The embryological characters of Cercidiphyllaceae:Unisexual flowers.The anthers are tetrasporangiate.The formation of the anther wall belongs to the Basic Type.The tapetum is glandular and most of its cells are binucleate.The microspore mother cells give rise to more tetrahedral tetrads than decussate tetrads by meiosis and the cytokinesis follows the simultaneous type.Degeneration takes place in some tetrads.When the anther wall dehisces,the mature pollens are 2-celled.Ovules are bitegmic and crassinucellate which originates from both of the primary parietal cell and the epidermal cells of the nucellus.No hypostase is formed.The megaspore mother cell gives rise to a triad.The chalazal megaspore functions and the development of embryo sac conforms to the Polygonum type.Three antipodal cells are ephemeral.2.The embryological characters of Eupteleaceae:Bisexual flowers.The anthers are tetrasporangiate.The formation of the anther wall belongs to the Basic Type.The tapetum is glandular and most of its cells are binucleate.The microspore mother cells give rise to more tetrahedrai tetrads than decussate tetrads by meiosis.Degeneration takes place in some tetrads and uninucleate pollens.When the anther wall dehisces,the mature pollens are 2-celled.The ovules are anatropous,bitegmic and crassinucellate,2-3 ovules exsits in the carples mostly.The outer integument is composed of 3-4 layers of cells,the inner integument is composed of 2 layers of cells,the outer integument thickens to 7 layers of cells in the micropyle end,the micropyle are formed by both the inner and outer integuments.Nucellar tissue is well developed,7-8 layers of nucellar cells densely arranged.3.The embryological characters of Troehodendraeeae: Bisexual flowers.The anthers are tetrasporangiate.The tapetum is glandular,in the subsequent development,the cells of the tapetum produce Ubisch body.The microspore mother cells give rise to tetrahedral tetrads.The stomium between the two pollen sacs grows invasively to each other,and finally leads to the dehiscence of the anther wall.The mature pollens are 2-celled.The ovules are anatropous,bitegmic and crassinucellate,the inner integument initiates first,followed by the outer one. As the development of the megasporal mother cell,the epidermal cell at the base of the nuceilus protrudes outward and then divides,finally the hood-shaped outer integument initiates.Systematies relationship based on embryological embryological features:1.Comparisons on the basis of embryological data indicate that Cercidiphyllaceae, Eupteleaceae,Trochodendraceae are unlikely to have close affinities with each other.There is considerable phylogenetic distance between them.2.The embryological characters support close relationship between Cercidiphyllaceae and Daphniphyllaceae in Saxifragales.Embryological features demonstrate Cercidiphyllaceae's highly unique.