542 SUMMARY OF CURRENT RESEARCHES RELATING TO 



development of the embryo is far advanced ; from one to nineteen nuclei 

 were found in a single antipodal cell. The lowest antipodal cell is often 

 very much enlarged. A remarkable embryo-sac was observed in a speci- 

 men of Aster undulatus, containing two oospheres and two endosperm 

 nuclei. The upper part of the sac is normal, but in the lower part just 

 above the first antipodal cell there is a cell and a large nucleus which 

 have the same structure and the same relative position as that of the 

 egg and the endosperm nucleus at the micropylar end. One of the 

 sperm nuclei has passed to the lower part of the embryo-sac to fuse with 

 the lower oosphere. This discovery of an antipodal, functioning as an 

 egg and about to be fertilised, has, the author considers, an important 

 bearing on the problem of the homologies of the antipodals. 



In the same species, A. undulatus, double fertilisation was observed. 

 The development of the embryo follows the type described for other 

 Compositee. 



Embryo-sac and Embryology of Nelumbo.* — H. H. York gives an 

 account of his work on the life-history of Nelumbo lutea. There is a 

 single hypodermal archesporial cell, and four megaspores are formed, the 

 lowest of which only is functional. An eight-celled embryo-sac is 

 formed, and usually one or more imperfect sacs, presumably derived 

 from sister megaspores. The antipodals are small and usually disappear 

 before the conjugation of the polar nuclei ; the synergids are small and 

 degenerate about the time of fertilisation. The fusion of the polar 

 nuclei is not complete until after fertilisation ; double fertilisation was 

 observed. An axial row of cells below the embryo-sac are large and 

 rich in protoplasm, and form a conducting passage for food from the 

 ower ovular tissue to the embryo-sac. The embryo-sac becomes divided, 

 after fertilisation, into three chambers by formation of two transverse 

 walls, and finally the whole sac becomes filled with endosperm. No free 

 cell formation occurs at any stage of the process. 



The history of the embryo is the same as reported by Lyon. A 

 spherical embryo of several hundred cells is formed ; no suspensor cell 

 is present. When the spherical embryo has reached its maximum growth 

 it becomes flattened at the outer end by the development of a collar-like 

 ridge extending about two-thirds of the way round. Development then 

 continues at the opposite side, giving rise to the two " cotyledonary " 

 lobes, which grow downwards very rapidly outside the endosperm. The 

 plumule forms a dome-shaped projection occupying a central position 

 between the lobes. Both the cotyledonary ridge and the stem tip 

 probably represent terminal structures, but on account of the spherical 

 form of the embryo it is impossible to trace the origin of any set of 

 cells which appear at the outer end of the more mature embryo, and the 

 cotyledonary ridge may be lateral. The first leaf and stem tip develop 

 side by side from the terminal mass of cells in the protuberance ; the 

 leaf arises on the side opposite the cotyledonary ridge. 



The author points out the similarity in early development between 

 the embryo of Nelumbo and those of certain Aroids {Lyskliiton and 

 others), while the development of the cotyledonary ridge shows a 



* Ohio Naturalist, iv. (1904) pp. 167-76 (3 pis.). 



