April 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 371 



important fact, that the nucleus of the embryo-sac is com- 

 parable to the nucleus of a male sporocyte, namely, the 

 pollen-mother-cell . 



If then the embryo-sac-cell is not a macrospore but a 

 sporocyte, then it must give rise to spores, and the question 

 arises, to how many spores ? 



As during the further development of the embryo-sac- 

 cell we find at successive stages, one, two, four, or eight 

 nuclei within the sac, vv^e might imagine that any one of the 

 four stages could correspond to the period of spore-formation, 

 i.e., that the sporocyte or embryo-sac-cell might give rise to 

 one, to two, to four., to eight spores respectively. Let us 

 consider these four possibilities : — 



If the sporocyte gave rise to only one spore, it would 

 have to be converted directly from the sporocyte-condition 

 into the spore-condition, and the eight nuclei within the 

 mature embryo-sac would have to be regarded as eight 

 nuclei of one prothallus developed from one spore. 



Against this interpretation the following objections may 

 be raised : — 



1. A direct conversion of one sporocyte ■ into one spore 



would have no analogue in the remaining vegetable 

 kingdom. 



2. The evident individuality of each half of the embryo- 



sac-cell after the division of the first nucleus, as 

 manifested by the micropylar end receiving its 

 nourishment from the degenerating periblem-cells, 

 while the basal end is fed by the plerome-elements 

 and by the formation of a plate on the basal surface 

 of the micropylar cell (see p. 363), point against our 

 accepting the two halves of the embryo-sac as belong- 

 ing to the same individual structure. 



3. The great constancy with which four cells arise in 



either end of the sac, also points to the two halves 

 of the embryo-sac being the homologues of one 

 another, and not vegetative and reproductive portions 

 of one prothallus. 



4. If, further, the apical half of the sac was a reproductive 



portion, while the basal half was a vegetative part, 

 how could we explain the conjugation of the two 

 primordial cells ? 



