372 TRANSACTIONS AND PROCEEDINGS OF [Sess. lvi- 



5. The cell-wall-forination round six of the nuclei is not 



in accordance with the normal way in which pro- 

 thallus-cells grow, but is, as we shall see later, quite 

 in accordance with the division of nuclei and the 

 subsequent cell-formation as they occur in other 

 sporocytes. 



6. We have no indication of changes in the sporocyte, 



which we could explain as being due to the supres- 

 sion or non-development of the remaining three 

 spores, supposing the division of a sporocyte into 

 four spores as the normal. 



May then the embryo-sac be the equivalent of two spores ? 

 If so, the first division of the nucleus of the sporocyte 

 (Strasburger's primary nucleus of the embryo-sac) would 

 have to be considered as the stage of spore-formation, and 

 the two groups of four cells within the embryo-sac would 

 correspond to two prothalli, namely, an apical one consisting 

 of the two synergidas, the ovum and the micropylar prim- 

 ordial cell, and a basal one consisting of the three antipodes 

 and the antipodal primordial cell. 



I shall discuss this two-spore hypothesis after having 

 explained what a four- and an eight-spore hypothesis would 

 lead us to. 



If the sporocyte gave rise to four spores analogously to 

 the way in which the male sporocyte or pollen-mother-cell 

 gives rise to four pollen-grains, then the first division of the 

 nucleus of the female sporocyte or embryo-sac-cell (figs. 16- 

 19) would correspond to the first of the binary divisions of 

 the male sporocyte, and the period at which four nuclei are 

 found in the sac (figs. 20-23) would correspond to the time 

 when the four pollen-grains are formed in the pollen-mother- 

 cell. 



We know that each of the four nuclei within the embryo- 

 sac redivides, figs. 24 and 25, and that thus they give rise to 

 differently named structures, namely : — 



1. One nucleus gives rise to the two synergidoe. 



2. „ „ to the egg-cell and micropylar 



primordial cell. 



3. „ „ to the two antipodes next the 



plerome-element. 



