170 



ANGIOSPERMS. 



the cell. The first nuclear division is heterotypic, corresponding in 

 detail with the first karyokinesis in the microspore mother-cell of the 

 same plant. The two resulting cells soon divide again, thus giving 

 rise to the axial row of four cells, the four potential macrospores. 

 The second nuclear division is the same as the second division in the 

 pollen mother-cell. A phenomenon which sometimes occurs in Helle~ 



borus (and it is probable that 

 it may take place in other plants 

 also) furnishes additional evi- 

 dence in support of our hy- 

 pothesis, namely, that the two 

 divisions in this hypodermal 

 cell, or embryo-sac mother-cell, 

 are homologous with the two 

 divisions in the pollen mother- 

 cell. Cell division may not 

 take place until after the second 

 nuclear division, when the four 

 granddaughter nuclei will lie in 

 the upper end of the cell, and 

 the cell-plates are laid down 

 simultaneously (Fig. 70, B). 

 It has been observed also that 

 the four nuclei, instead of lying 

 in one plane as in Fig. 70, B, 

 are sometimes arranged in a 

 tetrad and connected with each 

 other by a system of kinoplas- 



F,G. 7 o.-Embryo.sac mother-cell of HelUbor** j connecting fibers, as in the 



f&ticijts. 

 A, Upper portion of mother-cell showing nucleus in the Corresponding Stage of the pol- 



prophase of the first mitosis. 



B, same less highly magnified, showing the four poten- 

 tial macrospores ; in this case cell-division did not 

 follow first mitosis, and the plasma membranes mark- 

 ing out the four cells were formed simultaneously. 



len mother-cell. 



The lower cell of the axial 

 row becomes, as a rule, the 

 functional macrospore. It in- 

 creases rapidly in size at the expense of the other three cells and the 

 adjacent tissue of the nucellus, and develops in the usual way into the 

 embryo-sac. 



The unmistakable homology of the macrospore mother-cell of the 

 Angiosperms with that of the Gymnosperms has been very clearly 

 shown by Juel (1900). This author finds in Larix that the first and 

 second nuclear divisions in the macrospore mother-cell, which give 



