1914] MCALLISTER— EMBRYO SAC OF CONVALLARIACEAE 141 



are usually arranged more or less bilaterally. Although I was not 



memb 



from 



exam 



in the developing embryo sac of Lilium. In Maianthemum the 

 cell membrane extends out and joins with the lateral wall of the 

 mother cell, while all traces of the central spindle disappear. Later 

 the partition membranes degenerate, thus giving rise to a tetra- 

 nucleate cell (fig. 22). This tetranucleate cell enlarges by the 

 formation of vacuoles in its interior (figs. 23, 24), and its nuclei 

 undergo a further division to form the 8-nucleate embryo sac 

 (fig- 25). 



Streptopus roseus 



The first division of the megaspore mother cell of Streptopus 

 roseus results in the formation of 2 equal and fully separated 

 daughter cells (fig. 30). The inner cell enlarges, gradually com- 

 pressing the outer into a disorganized crescent-shaped mass (fig. 31). 



Before the outer cell has been completely disorganized, the 

 inner daughter cell divides, forming, in some cases at least, 2 fully 

 separated daughter cells (fig. 32). In most cases, however, the 

 partition wall is lacking, either not having been formed or having 

 degenerated after formation (fig. 35). It is of course impossible to 

 determine whether a partition wall is formed in all cases, but since 

 the evidence is clear that it is frequently formed, it seems reason- 

 able to expect that it is formed in all cases and subsequently under- 

 goes degeneration. 



Widely separated daughter cells such as are illustrated in fig. 

 33 are occasionally to be seen. While this wide cleft between the 

 cells is in this case, without doubt, due to plasmolysis, such a wide 

 separation could of course not have taken place had not the 2 cells 

 been perfectly distinct. Whether 2 such widely separated cells 

 can fuse to form a single binucleate cell may be doubted. Further 

 evidence on this point is to be seen in fig. 34. Here the nuclei of 

 2 homoeotypic daughter cells have each divided, forming 2 distinct 

 binucleate cells. The disorganized mass at the micropvlar end of 

 the outer cell is the remains of the outer cell of the first division* 

 A tendency is thus shown toward the formation of an embryo sac 



