April 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 377 



endosperm-cell must, however, in any case be regarded as a 

 true embryo, as it results from the union of two sexual cells. 

 It is destined to act as a storehouse for the stronger embryo 

 which develops from the cross fertilised egg-cell, — meaning 

 by cross-fertilisation, the fertilisation by an extraneous 

 sexual cell, i.e., a sexual cell derived from the anther-sac or 

 microsporangium of the same or of a different flower. 



My new interpretation of the embryo-sac does away also 

 with the suggestion that we might regard the micropylar end 

 of the embryo-sac as a female sporocyte, giving rise to four 

 macrospores, while the antipodal end was to be regarded as 

 a male sporocyte giving rise to four microspores, a conclusion I 

 stated thus : — " The egg-cell in the micropylar region receives 

 the contents of the pollen-tube and develops into the embryo; 

 it is therefore a true female cell, and its sister-cell I would 

 expect to be also a female cell, and I find that the nucleus 

 of the antipodal cell travels towards the nucleus of the 

 primordial micropylar cell, and that in Myosurus the two nuclei 

 meet in the micropylar half of the sac." 



Eeasons different from those I imagined lead to the 

 conjugation of the two primordial cells, the main of which I 

 believe to be hunger as has been pointed out already. Let 

 us study next, how this hunger is satisfied. 



C. Final Stage. 



Before commencing with our study of conjugation, it is 

 necessary to give a number of definitions of terms used : — 



The cell-plasm is that plasm of a cell outside the nuclear 

 membrane. 



The nucleus is the plasm between the nuclear and 

 nucleolar membranes. 



The nucleolus is the plasm within the nucleolar membrane. 



I have thus made the nuclear and the nucleolar mem- 

 branes the land-marks for the division of the protoplasm of 

 a cell into three zones, and have avoided classing the mem- 

 branes under any one of these three layers, although I am 

 inclined to consider the nuclear membrane as part of the 

 cell-plasm (after Strasburger), just as the nucleolar mem- 

 brane will probably have to be regarded as the innermost 

 portion of the nucleus, as will become apparent later on. 



We have already seen how the micropylar primordial cell 



TRANS. EOT. SOC. EDIN. VOL. XLS. 2 F 



