Studies on Embryology of Conyza canadensis (L.) Cronq

The microsporogenesis,megasporogenesis,the development of male gametophyte,female gametophyte,embryo and endosperm,and double fertilization of Conyza canadensis(L.) Cronq were studied in this paper.The results show as follows:the anther is tetrasporangiate and its mature wall comprises of an epidermis,endothelium,a middle layer and a single-layered tapetum;the epidermis degenerates;cells of endothelium persisted are columnar and with fibrous thick walls;the middle layer degenerates early and only a vestige can be observed at meiosis-I of microsporocyte;the tapetum belongs to glandular type,generally,is out of shape and degenerates early at meiosis-I of microporocyte;cytokinesis in the microsporocyte meiosis is of the simultaneous type,and the microspore tetrads are tetrahedral or isobilateral;pollen grains are mainly 3-celled,and occasionally 2-celled;the ovary is bicarpellate,unilocular,one ovules and basal placenta;the ovule is unitegmic,tenuinucellate,anatropous and with developed endothelium;archesporial cell of megaspore differentiates immediately below the nucellar epidermis and functions as megasporocyte after development,and then,the megasporocyte undergoes meitotic to form a linear tetrad,only one chalazal megaspore in linear tetrad becomes the functional megaspore;the embryo sac is of the Polygonum Type;two polar nuclei melt into a secondary nuclei before fertilization;fertilization is porogamous;the development type of the endosperm is Nuclear Type,and the embryogeny belongs to the Asterad Type;endosperm haustorium is present.