小蓬草的胚胎学研究

对小蓬草(Conyza canadensis)大小孢子发生、雌雄配子体形成、受精、胚及胚乳发育过程进行了研究,主要结果如下:花药四室,药壁由表皮、药室内壁、中层和绒毡层组成.表皮退化;药室内壁宿存,细胞柱状伸长,纤维状加厚;中层细胞退化较早,在小孢子母细胞减数分裂开始时仅存残迹;绒毡层于小孢子母细胞减数第一次分裂前期开始原位变形退化,属于腺质型绒毡层;小孢子母细胞减数分裂为同时型,四分体的排列方式主要为四面体形和左右对称形;成熟花粉粒多为3细-胞花粉粒,偶见2细-胞花粉粒.子房下位,2心皮,1室,单胚珠,基生胎座;单珠被,薄珠心,倒生胚珠,具发达的珠被绒毡层.珠心表皮下分化出大孢子孢原细胞,孢原细胞直接发育为大孢子母细胞,大孢子母细胞减数分裂形成4个大孢子直线形排列,仅合点端的大孢子发育成功能大孢子母细胞,胚囊发育为蓼型.两个极核在受精前融合为次生核,珠孔受精.胚乳发育属于核型,胚胎发育为紫菀型;具胚乳吸器.

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.