1917] WEN IGER— EUPHORBIA 273 



to be little possibility for self-pollination, for the neck of the cya- 

 thium is very small and the staminate flowers do not extend above 

 the surface of the cyathium. When the embryo sac is mature, 

 the staminate flowers are still rudimentary. Insect pollination is 

 improbable because of the smallness of the cyathium and the 

 smallness of the opening. Seeds are formed with marked regularity, 

 which would hardly be the case if wind pollination occurred. 

 Hegelmaier (6, 7) found the same conditions with regard to pollina- 

 tion in E. dulcis. 



Embryo 



The fertilized egg divides in a plane parallel with the long axis 

 of the sac (fig. 20). The second division occurs at right angles to 

 the plane of the first (fig. 21). Further divisions result in the 

 formation of a globular mass of cells (figs. 22, 23, 24). In all cases 

 observed, the embryo formed no suspensor. The beak of the 

 nucellus and the obturator gradually disintegrate as the embryo 

 is formed, and the inner and outer integuments grow so as nearly 

 to fill the large opening originally constituting the micropyle, 

 but still leaving a small opening (fig. 25). 



As early as the 2-celled stage of the embryo, endosperm nuclei 

 appear at either side of the embryo. In the case represented in 

 fig. 20, one endosperm nucleus (en) lies between the embryo and 

 the micropylar end of the sac. The endosperm nuclei increase 

 rapidly in number and are distributed quite uniformly throughout 

 the peripheral region of the sac (fig. 24). Cell division does not 

 occur in the endosperm until the embryo has come to consist of 

 several hundred cells. The endosperm gradually fills the space 

 originally occupied by the nucellar tissue (fig. 25, n). 



The embryo changes as it grows from a globular (fig. 26) to an 



* 



elongated form (figs. 28, 29). Fig. 30 shows the earliest stage at 

 which cotyledons were observed. A well developed root cap is 

 present in the mature embryo (figs. 27, 31, re). When mature, the 

 embryo (figs. 27, 31) is straight and its length nearly equals that of 

 the seed, the root cap (re) being pressed closely against the micro- 

 pyle. Surrounding the embryo, except at the tip of the root cap, 

 i> the endosperm (fig. 27, end), whose cells contain a large amount of 

 reserve food material in the form of starch, fat, and aleurone grains. 



