146 BOTANICAL GAZETTE [august 



In those forms in which more than one reduction nucleus enters 

 into the structure of the embryo sac, we find various degrees of 

 separation of these nuclei in temporary cells. In Smilacina stellata 

 and S. sessifolia and in Maianthemum canadense the 4 reduction 

 nuclei become fully separated by cell membranes, which later 

 disappear. In Smilacina racemosa, w r hose embryo sac arises from 

 the outer of 2 daughter cells, the homoeotypic nuclei are for a time 

 fully separated from one another by split cell plates. In S. amplexi- 

 caulis definite cell plates are present between these homoeotypic 

 nuclei, and it seems probable that an examination of sufficient 

 material would show the splitting of these cell plates. In Strepto- 

 pus roseus, whose embryo sac arises from the inner daughter cell of 

 the first division, a definite cell plate is formed which, at times at 

 least, splits, thus causing complete separation of the 2 homoeotypic 

 nuclei. The single cell membrane in the developing embryo sac of 

 Convallaria majalis (24) and the cell plates in Medeola show the 

 tendency here toward the separation of the products of the reduc- 

 tion divisions into distinct cells. 



There seems to be substantial agreement that in cases where one 

 cell of an axial row of 4 develops into the embryo sac, the 4 cells 

 are to be regarded as megaspores, and the cell from which these 

 have arisen a megaspore mother cell. Both megaspore mother 

 cell and megaspore are regarded as the morphological equivalents 

 of the microspore mother cell and microspore respectively. In 

 those cases, however, in which the embryo sac develops from one of 

 the 2 daughter cells of the megaspore mother cell or from the 

 undivided megaspore mother cell, in general two opposing views are 

 prevalent. The one, elaborated by Coulter (10), regards reduc- 

 tion as a criterion by which spores or spore nuclei may be identified, 

 and holds that even though the reduction nuclei are not separated 

 they should nevertheless be regarded as megaspore nuclei. The 

 other view, probably most actively supported by Campbell (6, 7) 

 and Brown (3, 4), holds that reduction is not the "sole criterion 77 

 for distinguishing spores and gametophytes, and that the cell giving 

 rise to the embryo sac should be regarded as a megaspore, whether 

 it is the undivided megaspore mother cell, one of 2 daughter cells, 

 or one of 4 daughter cells. 



