128 Taylor — A Morphological and Cytological 



sorbing the two upper; its large nucleus soon divides, and the 

 resulting nuclei move away from each other toward the opposite 

 ends of the cell (fig. 5). The further behavior of these nuclei 

 is similar to that which obtains in all known embryosacs of 

 angiosperms." From his figures it seems evident that the "upper 

 cell" means the one near the micropyle, and the "lower cell" 

 the one near the chalaza. His description would indicate that 

 the more micropylar cell goes through the homotypic division 

 before there is any division in the more chalazal cell, and that 

 following this division a wall is laid down and then the two cells 

 thus formed degenerate. The homotypic division in the chala- 

 zal cell of the pair then follows, and both of the nuclei formed 

 function in the maturation of the embryosac, each dividing 

 twice to give the eight elements of the mature sac. It appeared 

 to the writer an unusual circumstance that one cell of the orig- 

 inal diad should go through a complete homotypic division 

 only to degenerate, whereas in the other the nucleus only should 

 divide and both nuclei function. In view of the more recent 

 work in cytology it seems more to be expected that one of the 

 cells of the original diad should degenerate without dividing, 

 and that if the homotypic division in the other cell closed with 

 wall formation, the daughter cell adjoining the degenerating 

 cell should also break down. This would account for the two 

 degenerating cells reported by Mottier, and would indicate 

 that the nucleus in the remaining cell, morphologically equiva- 

 lent to one cell of a tetrad, would have to pass through three 

 successive free gametophytic divisions before the embryosac 

 reached maturity, which is rather the normal history in dicoty- 

 ledons. However, if Mottier actually saw the process of divi- 

 sion of the micropylar cell of the diad, this history could not 

 hold. But he does not figure any stage during the division, 

 and it is easily possible to misinterpret the condition if only the 

 final product of a row of three cells is available. The significant 

 difference between the two possibilities lies in that in the one 

 case only two gametophytic divisions occur, showing a tendency 

 toward the Lilium type where but one is present, while in the 

 second case the more normal number of three would be found. 

 The question as to whether a cell which is to undergo degenera- 

 tion is likely to divide earlier and in a more primitive manner 

 (i. e. } with wall formation) than its sister cell which is to 



