BOT.-VOL. I.l CAMPBELL—SPA RG A NIUM. 31$ 



of the young embryo. Its absence in Sparganium, the 

 Gramine^, and such Aroids as have been examined is no 

 doubt to be sought in the better development of the endo- 

 sperm in these forms, and possibly also in the presence of 

 numerous antipodal cells, which assume temporarily the 

 functions of the endosperm. 



The first division of the primary endosperm-nucleus occurs 

 almost immediately after fertilization. At this time the 

 endosperm-nucleus is, usually at least, near the antipodal 

 end of the sac. The divisions are repeated until there are 

 formed in the usual manner many free nuclei arranged in a 

 single layer in the parietal cytoplasm (fig. 30). These 

 nuclei are more or less flattened and possess a single 

 large nucleolus. At the apex of the sac they are more nu- 

 merous, and the cytoplasm is more abundant and quite sur- 

 rounds the young embryo. As usual, the first cell-division 

 in the endosperm takes place at the apex and proceeds to- 

 ward the antipodal region. 



While the endosperm-nuclei have been dividing, and 

 the peripheral layer of protoplasm is still very thin, the antip- 

 odals have increased enormously in bulk and divided rap- 

 idly to form the large mass of cells found at the antipodal 

 end of the sac. We have already spoken of the karyoki- 

 netic division of the antipodal nuclei and it is very doubtful 

 whether even in the binucleate cells sometimes found in the 

 later stages this division is ever direct, as it has been found 

 to be in the enlarged antipodal cells of a number of plants 

 (e. g. in Ranunculaceae, Mottier, 1895). As the embryo-sac 

 enlarges it changes its form somewhat in S. simplex, becom- 

 ing relatively much narrower at the upper end which early 

 becomes completely filled with endosperm (fig. 37). 



In the micropylar end of the sac the protoplasm early be- 

 comes much denser, the nuclei are larger than at the sides 

 of the sac and not confined to a single layer. The nuclei 

 increase a good deal in size before the cell-walls are formed 

 between them (fig. 57). 



As Sparganium simplex shows very clearly the endosperm 

 formation, this was studied in some detail. Before the divi- 

 sion-walls are evident, the nuclei are arranged at nearly equal 



