THE FEMALE GAMETOPHYTE 



89 



great obscurity, and very little has been added to the original 

 suggestions concerning it. 



The most important departure from the ordinary history 

 is that shown by Peperomia pellucida, as described by Camp- 

 bell 70 and Johnson 70 (Fig. 38), Gunnera (Schnegg 103 ), Tril- 

 lium (Ernst 116 ), and Tulipa as described by Guignard. 890 In 

 Peperomia the nuclei of the embryo-sac do not show any of the 

 polarity that is so marked a feature in other forms. The first 

 four nuclei are large, and arranged peripherally like the spores 

 of a tetrad. Divisions continue until sixteen parietal nuclei, 

 rather evenly distributed, are found in the sac. One of the 

 nuclei at the micropylar end of the sac becomes somewhat larger 

 and is surrounded by a fairly defined mass of cytoplasm with a 

 limiting membrane, this cell functioning as the egg. Another 

 micropylar cell is similarly organized, and from its position 



c 



D 



Fig. 38. — Peperomia pellucida. A, longitudinal section of an ovule with a four-nucleate 

 embryo-sac showing no polarity ; x 295. £, embryo-sac at time of fertilization ; t, 

 pollen-tube; o, oospore; «, group of nuclei fusing to form endosperm nucleus; p, 

 peripheral nucleus of embryo-sac ; s, synergid ; », vacuole ; x 520. C ', D, groups of 

 nuclei fusing to form endosperm nucleus ; x 520. — After Johkson.™ 



may be called a synergid. Eight of the remaining nuclei mass 

 together, are surrounded by a common cytoplasmic investment, 

 and after fertilization unite to form a great fusion-nucleus that 

 functions as the primary endosperm nucleus. The remaining 

 six nuclei remain in their parietal position and are finally cut 



