THE CARPEL AND OVULE 299 



group ; those at the micropylar end form the egg-apparatus. The 

 latter consists of the two synergidae which occupy the extreme apex, 

 and the ovum attached rather lower. The odd nuclei from each end 

 approach one another, and finally coalesce (vi, vii) to form the central 

 fusion-nucleus. The embryo-sac is then ready for fertilisation. 



All the nuclei resulting from this development of the contents of 

 the embryo-sac are haploid. Reduction has already taken place in 

 the divisions of the mother-cell. The embryo-sac, or megaspore, 

 being one of the products of that operation, its nucleus is already 

 reduced. The whole group of nuclei, together with the cytoplasm 

 that surrounds them, may be recognised as the sexual phase or gameto- 

 phyte. It is characterised by differing in the constitution of its nuclei 

 from the ordinary vegetative cells of the plant : all its cells are 

 primordial cells, that is, they are not surrounded by cell-walls, but 

 are delimited by plasmatic films. The Ovum is that cell of the 

 gametophyte which will be fertilised. It is the female gamete, or 

 sexual cell, which is to take part in sexual reproduction. 



