1914] MCALLISTER— EMBRYO SAC OF CONVALLARIACEAE 145 



It is probable that little significance is to be attached to these 

 abnormalities. The occurrence of more than one megaspore mother 



common 



has been rather remarkable that more have not been found among 



m 



As will be seen from figs. 11, 12, 17, and 18, the ovules in which 

 2 mother cells or 2 embryo sacs have been figured are all con- 

 spicuously broader than those containing but one mother cell. The 

 relative proportion of the sterile tissue in the two cases is essentially 

 the same, thus suggesting that where a normal amount of sterile 

 tissue is present but one mother cell is formed. 





Discussion 



It will be seen from the foregoing that within the limits of the 

 Convallariaceae considerable variation exists as to the origin of the 

 embryo sac. In Polygonatum commutatum and in Trillium recurva- 

 tum (9) the embryo sac arises from one of an axial row of 4 mega- 

 spores. In Clintonia borealis (23) it arises from the outer of 4 

 megaspore nuclei, which are, however, not separated by cell walls 

 or membranes. In Smilacina racemosa and in S. amplexicaulis 

 it has its origin from the outer daughter cell of the first division of 

 the mother cell; while in Streptopus roseus, Trillium grandijlorum 

 (13), and Paris quadrifolia (13) the embryo sac arises from the 

 corresponding inner daughter cell. In Smilacina stellata, S. sessi- 

 folia, and Maianthemum canadense 4 fully separated megaspores, 

 by the disappearance of the partition walls, become merged in one 

 tetranucleate cell. One division of each of these 4 nuclei forms the 

 8 nuclei of the complete embryo sac. The immature embryo sac of 

 Convallaria majalis, according to Wiegand (24), has a single cell 

 membrane separating the inner pair of reduction nuclei from the 

 outer pair, and in Medeola virginica a pronounced cell plate is 

 developed between the daughter nuclei of the first division of the 

 mother cell, which, however, disappears before the second division, 

 and definite though temporary cell plates are also formed between 

 the homoeotypic nuclei. Thus it will be seen that in this group, 

 one, two, or four of the reduction nuclei may enter into the structure 

 of the mature embryo sac. 



