Abstract: Using scanning electron microscopy and semi-thin plastic sections, the pattern of development of the rice ( Oryza sativa L. ) embryo from 2 days after pollination (DAP) to maturity was followed. ( 1 ) At 2 DAP, the young embryo was observed to consist of an embryo proper, a hypoblast and a suspensor. The trum-pet-shaped hypoblast was a transitional region situated between the suspensor and the embryo proper. To label the hypoblast as suspensor is incorrect. During this time, dorsiventrality was established, but a radicle was not yet differentiated. Therefore it is still referred to as a proembryo. (2) 3 ~ 5 DAP, the embryo underwent definite morphological and anatomical changes. In the young embryo at 3 DAP the scutellum and colcoptile appeared simultaneously directly from the proembryo. The coleoptile did not originate from the scutellmn. During these foremost 3 days, the coleoptile primordium underwent a special kind of morphological change and formed a young coleeptile having the shape of an inverted hollow cone. This process revealed the true mechanism of c61eeptile formation. Anatomical observation indicated that the embryo at 3 DAP began to differentiate procambium, ground meristem and root cap. At 4 DAP a dome-like growth cone and protoderm of radicle appeared. Then the shoot-root axis became established. At 5 DAP the plumule, hypocotyl and radicle were formed. (3) It was shown that the embryo of rice actually has two cotyledons: the scutellum (a part of the embryonic envelope) and the coleeptile (The scutellum being the lateral cotyledon, a part of outside cotyledon, and the coleoptile the apical cotyledon--the coleoptile may be considered to be a modified form of a cotyledon). This kind of structural arrangemem can be referred to as dimorphic cotyledon.

Key words: Rice embryo development, Scutellum and coleeptile, Hypoblast, Dimorphic cotyledon, Dorsiventrality, Embryonic envelope