Studies On The Embryo Of Gnetum Montanum Markgraf

The methods and data of phytomorphology. phytotomy, phytoembryology. palynology. phytocytota.xonomy. phytochemistry and molecular systematics are referred to summarize the systematic status of the genus Gnetum in this paper.The embryology in G.montanum was studied using light microscope and scanning electron microscope in this paper. The main results are as follows:1. G. montanum is dioecious with spike inflorescence. The abortive ovules and male flowers in male cone inflorescence and the ovules in female cone inflorescence are originated from an annular meristem which differentiates from the base of each collar.2. The anther wall of G.montanum conforms to the basic type, which consists of epidermis, middle layer and tapetum. Most cell of the tapetum contains 2 nuclei, the middle layer and the tapetum are absorbed during microsporegenesis. The cytokinesis of the microspore mother cells in meiosis is synchronous. Matural pollen grains are 3-celled structure of the tube nucleus, the generative cell and prothallial cells.3. The ovule is orthotropous and crassinucellate, nucellus is surrounded by three envelopes. There are a lot of free nuclei in female gametophyte. Before fertilization, there are no indeed egg cell differentiated from the free nuclei. The pollen tube enters the female gametophyte from micropylar end and the free nuclei near pollen tube have the average chance to acting as the functional egg.It is the first time that these phenomena were observed: Two nuclei are surrounded by plasma and locate at the central of the female gametophyte and the others nuclei are positioned at the fringe of the female gametophyte; Before the pollen tube enters the female gametophyte. the nuclei in chalazal end begin splitting of plasma and form multinuclear cell.4. The pollens of Gnetumc are spherical or applanate with single aperture. The ornamentation of exine is spine. The basis part of spine is lenience and the top part of spine is tip or obtuse sphere. The characteristics of pollen grain are related with the distribution of Gnetum and classified system of subgenus.5. According to Bract Scale and Seed Scale Complex(BSSC) theory and the observation results in this experiment, the author considers that the Gnetum genus belongs to the evolvement line ofBSSC. and is more closer to conifers than other seed plant.