44? BOTANICAL GAZETTE [December 



tegumentary tissue fully surrounds the megaspore mother cell, even 

 as early as the time of the reduction division (fig. 1 2) of the mother 

 cell. The greatly elongated mother cell forms the four potential 

 megaspores (fig. 13), of which the three potential micropylar mega- 

 spores soon degenerate, while the fourth or functioning one forms 

 the embryo sac. 



The nuclei of the three degenerating cells (fig. 14) soon dis- 

 appear, while that of the functional megaspore is clearly visible. 

 In degenerating, the potential megaspore cell next to the functional 

 megaspore disappears first; for a time it forms a sort of cap upon 

 the functional megaspore cell. The three degenerating cells stain 

 very heavily, while the megaspore cell stains lightly. These 

 degenerating cells, which stain deeply with safranin, are last 

 observed as a strip of red above the functional megaspore. 



Nucellus 



« 



While the megaspore mother cell is being formed (fig. 11), a 

 layer of nucellar tissue envelops it. The rapidly developing integu- 

 ment soon surrounds the nucellus and its mother cell. The cells 

 of the nucellus are long and narrow, and their transverse walls 

 are usually oblique. 



A similar tissue arises in many of the other species of the 

 Scrophulariaceae. Balicka-Iwanowski (i) calls it '^nucelle," 

 and figures such a tissue in Uroskineria spectahilis, Barisia alpina, 

 Pedicularis palustris, Klugia notoniana, Campanula rotundifolia, 

 and Marina longifolia. 



The contents of these cells stain with Delafield's haematoxylin 

 less heavily than the four megaspore cells, and less than the cells 

 immediately surrounding them. As the embryo sac forms, it 

 pushes its way through the micropylar end of the nucellus layer, 

 and when the embryo sac is fully formed the nucellus is found 

 surrounding only the chalazal end of the sac. The nucellus dis- 

 appears while the endosperm is being formed within the embryo 

 sac. It is still apparent when the first division of the endosperm 

 nucleus takes place, and also until after four cells of the endosperm 

 have been formed. Cells of the nucellus were not observed to be 

 present in later developments of the endosperm (fig. 25). 



