Development of Embryo Sac and Embryo in Euphorbia preslii and E. splendens

Abstract

1. The cyathium of both species studied begins as a papilla which arises between two bracts. The order of appearance of the parts of the cyathium is as follows: staminate flowers, involucre, ovules, carpels, and secondary staminate flowers which arise as branches of the first set. 2. The megaspore mother cell is subepidermal in origin in E. Preslii, and probably also in E. splendens. 3. An axial row of 4 megaspores is formed, the lowest of which develops into the embryo sac; the other 3 spores disintegrate. 4. The inner integument begins to develop before the outer, but the latter grows rapidly and soon overtops the inner. 5. The mature embryo sac is long and narrow, and is deeply imbedded in the tissue of the nucellus. In E. Preslii it has the structure usual in angiosperms. In E. splendens there are peculiarities in the history of the antipodal nuclei which require further study to make definite conclusions possible. It seems probable that each of the 4 antipodal nuclei may undergo a second division. 7. The obturator arises as an outgrowth of the placenta. It fills the space between the beaklike prolongation of the nucellus, the placenta, and the ovary wall. Its cells disintegrate after the embryo begins its development. 8. At about the time of the first division of the egg of E. Preslii, endosperm nuclei come to lie between it and the micropylar end of the embryo sac. 9. The embryo becomes a round mass of cells; this mass elongates and later 2 cotyledons and a well developed root cap are formed. The mature embryo is straight, and, except at the tip of the root cap, is surrounded by the endosperm. In E. Preslii no suspensor was observed; in E. splendens there is a short suspensor.