1914] MCALLISTER— EMBRYO SAC OF CONVALLARIACEAE 147 



It seems clear that these two views are due to a difference in the 

 usage of the terms "megaspore mother cell" and "megaspore," 

 rather than to any misunderstanding or misinterpretation of the 

 data. That the megaspore mother cell of Lilium has a function 

 similar to that of the inner megaspore of the row of 4 in Polygonatum 

 may be the case, inasmuch as both give rise to the embryo sac, but 

 the mother cell in the first case has arisen from the tissue of the 

 nucellus, in the same position and by almost identical cell divisions 

 as in Polygonatum. Aside even from any consideration of the 

 reduction phenomena, there would seem to be no doubt as to the 

 strict homology of the megaspore mother cells in these two forms 

 on the basis of their position in the nucellus, their conspicuous 

 size, the character of their protoplasm, and the mode of their 

 differentiation from the tissue of the nucellus. This conclusion 

 applies equally well to the megaspore mother cells of most other 

 angiosperms. The fact that the heterotypic division occurs in the 

 megaspore mother cell of Lilium may be regarded as confirmatory 

 evidence of its nature. 



mbry 



mega 



of Polygonatum. These 4 nuclei in the above-mentione 

 are homologous, whether we call them " megaspore nuclei" or "the 

 first 4 nuclei of the embryo sac." The increasing number of cases 

 in which the first 4 nuclei arising from the megaspore mother 

 cell are found to be more or less separated by temporary cell 



membranes 



manner, namely the loss by the 4 mega 



of their physiological individuality as spores and the subsequent 



membranes 



stage of the embryo sac. 



In Smilacina stellata (18) I have shown that the 4 reduction 



com 



wide clefts between the cells are often present. This separation 

 is due probably to shrinkage in fixation. The cell membranes 

 cannot be regarded in the same light as evanescent cell plates, for 

 here the cell plates are completely formed, after which they split 

 to form the distinct membranes of the new cells. There can be no 



