THE OVULE OF IMPATIENS 201 



sac becomes larger and elongated (fig. 1, K), and subsequent di- 

 visions produce the usual eight nuclei. The antipodals cannot 

 be distinguished with certainty, and are evidently transitory, as 

 they are in Euphorbia, Salix, Alyssum, Acer Habernaria, Casuarnia 

 and many others. The egg apparatus has a peculiar form, the 

 egg being next to the micropyle and the synergids below it as in 

 Spirea japonica. The egg is nearly spherical with a central nu- 

 cleus, the synergids have the usual more or less oval form (fig. 

 2, 0). The apparatus lies at some distance from the mycropyle. 

 The fusion nucleus lies just below the embryo at the time of di- 

 vision (fig. 3, U). The polar nuclei did not appear in the sec- 

 tions with the egg apparatus represented in figures 2, O and P. 



Just what occurs in fertilization is not clear. The pollen tube 

 reaches a spot between the egg and one of the synergids, and a 

 sperm nucleus may be seen in the tube, but the process could 

 not be traced further. Fertilization probably takes place before 

 the fusion of the polar nuclei. The peculiar structure which 

 looks like a second pollen tube in contact with the synergid to 

 the left (fig. 2, P) was not as distinct as the true tube represented 

 in the figure, its clearness being somewhat exaggerated in the 

 drawing. Its significance is not evident, but it suggests a pos- 

 sible branching of the pollen tube such as is found in some forms. 



In the nuclear di\dsion which occurs in the embryo-sac the 

 gametophyte number of chromosomes seems to be twelve. It is 

 particularly clear in the first division (fig. 1, K). 



The primary endosperm nucleus divides before the egg (fig. 

 2, P), the micropyle widens near the egg and a little of the cyto- 

 plasmic contents of the embryo-sac fill in the space. Thus the 

 position of the haustorium is indicated before the suspensor is 

 formed. The endosperm nucleus divides rapidly, forming a 

 thick jacket around the developing embryo and lining the sac. 

 The Ulterior of the sac is nearly filled with endosperm when the 

 embryo has reached the spherical stage. Several endosperm nu- 

 clei appear in the cytoplasm in the micropyle at this stage. The 

 nature of the haustorium here becomes apparent. As the em- 

 bryo develops the endosperm gradually disappears until it is 

 entirely displaced. There is no endosperm in the seed. 



