214 Campbell: The embryo-sac of Pandanus 



tained two nucleoli, and one of these nuclei looked as if it pos- 

 sibly might have been the result of the fusion of two. 



Owing to the similarity in the appearance of the nuclei of the 

 nucellus-cells adjacent to the young embryo-sac and those of the 

 sac itself, the former may sometimes be mistaken for those belong- 

 ing to the embryo-sac, but in the later stages the much greater 

 size of the embryo-sac nuclei makes it very easy to recognize 

 them. However, a structure is occasionally met with that is at 

 present not quite clear. There is sometimes found a small cell 

 (figs. 13, 15, j) apparently cut off from the side of the embryo- 

 sac, recalling the small cells of similar appearance cut off from 

 the sac in Peperomia, The contents of these cells are densely 

 granular like those of the embryo-sac, but the nuclei are usually 

 small, and I am inclined to believe at present that these cells 

 really belong to the nucellus and have pushed into the cavity of 

 the embryo-sac somewhat in the same fashion as those already 

 mentioned as sometimes pushing up from below. The occasional 

 occurrence of a small nucleus apparently free In the cytoplasm of 

 the sac, and differing in appearance from the other nuclei, sug- 

 gests that possibly the wall of this intruding cell may have become 

 resorbed, discharging the nucleus into the embryo-sac. These 

 points cannot be settled, however, until the history of the nuclear 

 division is known. 



All of the cells surrounding the embryo-sac differ more or less 

 from the outer nucellar tissue, having more watery contents and 

 sometimes rather larger nuclei. They are probably concerned to 

 some degree with the nutrition of the embryo-sac, and sometimes 

 this central mass of tissue suggests a mass of sporogenous cells ; 

 and it is not impossible that it really may represent a mass of 

 sporogenous tissue of which only one cell gives rise to the spores. 



Various attempts" have been made to explain, as modifications 

 of the ordinary angiospermous embryo-sac, the peculiar conditions 

 found in Peperomia and the other forms with a double number of 

 nuclei. Johnson and Brown both believe that the embryo-sac 

 in Peperomia represents four megaspores and not a single one ; 

 and Coulter * in a recent paper maintains that the embryo-sac 



* Coulter, J. M. Relation of megaspores to embryo-sacs in angiosperms. Bot. 

 Gaz. 45 : 361-366. 1908. 



