Johnson : Development of Saururus cernuus L 367 



At about the time that the primary archesporial cell becomes 

 distinguishable the development of the inner integument begins. 

 This is soon followed by the outer integument, arising in the same 

 way from the surface cells at the base of the nucellus ; both in- 

 teguments closing in to form the micropyle at about the time the 

 macrospore begins to encroach on its sister cells. The first 

 division of the macrospore is transverse, and the following divisions 

 apparently occur in the normal manner, as we find a little later 

 an eight-nucleate and then a typical seven-nucleate embryo-sac 



(Fig. i). The oosphere is rather clear or with large vacuoles, 

 while the synergids which also have definite walls, have much 

 denser contents {eg, Fig. i). The polar nuclei fuse near the middle 

 of the embryo-sac to form a nucleus twice the size of the egg nucleus 

 (ipn % Fig. i). The antipodals are apparently quite normal at first, 

 each with a darkly staining nucleus, but they soon become flattened 

 against the base of the embryo-sac. Then their nuclei disorganize 

 and the antipodals are no longer distinguishable, probably playing 

 no further part {ant, Fig. i). 



After the seven-celled embryo-sac is formed it grows rapidly, 

 especially in length, breaking down the tissue of the enlarging 

 nucellus till it reaches two-thirds of the way to the base of the 

 latter (Fig. 4), a length of 250 micromillimeters. Finally it 

 broadens at the base, remaining narrow at the top, assuming thus 

 the shape of a long-necked flask, with the egg apparatus at the 

 top and the endosperm nucleus at the base of the neck. 



It is evidently at about this time that fertilization occurs, for 

 soon after this the endosperm nucleus divides. One of the 

 daughter nuclei remains in the neck while the other moves down 

 into the body of the flask, and then a wall is immediately formed 

 across the base of the neck giving rise thus to two endosperm 

 cells {epn, Fig. 4). From this time on the upper nucleus divides 

 frequently, a cell wall forming immediately each time, and the neck 

 of the embryo-sac thus becomes filled with a number of endosperm 

 cells before any change is perceived in the egg or synergids {ep, 

 Fig. 5). The lower of the first two endosperm nuclei grows to a 

 very large size (epn, Fig. 5), but never divides further. It lies in 

 a thin layer of cytoplasm near the wall of this large, lower en- 

 dosperm cell and seems to control the advance of the latter upon 



