118 EGG-APPARATUS, ETC. [CH. 



we see these cells becoming disorganised and collapsed, 

 and their swollen remnants gradually disappearing. 



As this goes on, the single nucleus of the embryo-sac 

 divides, and each daughter-nucleus with its complement 

 of cytoplasm passes to the opposite ends of the sac, a 

 large vacuole appearing between them. At each pole, 

 enlargement and nutrition proceeding, each nucleus 

 divides again, and so produces two nuclei at either end ; 

 and there each of the pair undergoes a further division 

 at right-angles to the last, making eight nuclei in all 

 four at each end. 



Then one nucleus from each polar four passes slowly 

 towards the centre of the sac, in the cytoplasm, where 

 they come into contact, and sooner or later fuse more or 

 less completely, and form the embryo-sac nucleus. One 

 of the upper three nuclei then rounds off as the oosphere, 

 while its two neighbours form a pair termed the syn- 

 ergidce; and the three nuclei at the basal end obtain 

 these cell-walls round their investing protoplasm and 

 form the so-called antipodal cells. The synergidas and 

 oosphere constitute the " egg-apparatus " of the embyro- 

 sac, and the ovule is now mature, and its oosphere ready 

 to receive the nucleus and protoplasm brought to it by the 

 pollen-tube that is to say, it is ready for fertilisation. 



The differences met with in various types of Angio- 

 sperms from the above description refer to details only, 

 but in the Gymnosperms some of these details are of 

 fundamental importance, and must be carefully noticed. 



The origin of the carpel and the hump of embryonic 

 tissue on it, which is to form the nucellus, follows 

 essentially the same course ; and the assumption of the 

 anatropous position, uprising of the integument, and 

 formation of the micropyle also present no features re- 

 markably different. 



