掌叶大黄胚胎学研究

掌叶大黄(Rheum palmatum L.)的花药4室,单或复孢原。药壁发育为单子叶型。腺质绒毡层发育后期出现双核。小孢子四分体为四面体型,胞质分裂为同时型。成熟花粉为3细胞,表面具3条沟。子房1室,单胚珠,直生,两层珠被,由内珠被形成珠孔,厚珠心。单孢原,位于珠心表皮下。直线形或T形大孢子四分体。合点端的大孢子发育为蓼型胚囊。2个极核在受精前合并为次生核。3个反足细胞宿存。胚乳发育为核型,在球形胚末期开始形成细胞。合点端的胚乳核一直不形成细胞,而为游离核的胚乳吸器。在胚乳吸器和其它部位都发现胚乳核融合现象。胚的发育属于紫菀型。胚具小胚柄。成熟胚囊时期出现承珠盘,且存留时间很长,成熟胚期尚存痕迹。

EMBRYOLOGICAL STUDIES IN RHEUM PALMATUM L.

Embryology of Rheum palmatum L. has been studied. The main results are as follows. 1. The anther is four sporangiate with monoor multicellular archesporium. The development of anther walls conforms to the monocotyledonous type. The cells of the glandular tapetum be- come two nuclei in the later stage. The microsporocyte undergoes simultaneous meiotic divi- sion and produces tetrahedral tetrad. The pollen grains with three furrows are shed at the 3- celled stage. 2. The ovary is unilocular and contains only one ovule, bitegmic and crassinu- cellate. The micropyle is formed by the inner integument. The develoment of embryo sac conforms to the Polygonum type. The single hypodermal cell in nucellus functions as arches- porium. The megaspore mother cell undergoes meiosis to form a linear or T-shaped tetrad. Only the chalazal megaspore functions and forms the female gametophyte, whereas the other three degenerate. Two polar nuclei fuse before fertilization takes place. Three antipodal cells persist up to globular embryo stage. 3. The endosperm is of nuclear type. Endosperm nuc- lei form cells since the later stage of the globular embryo. However the chalazal endosperm nuclei do not form cells. They form a free nuclei endosperm haustorium. The phenomenon of free nuclei fusion has found in the haustorium and other part of the embryo sac. The de- velopment of embryo belongs to the Asterad type and the embryo has a small suspensor. 4. The hypostase appears at the stage of the mature embryo sac. It persists for a long time and only leaves a trace at the organized embryo stage.