4 Transactions. 



The basal cell is now cut off at the base, and the central cell 

 ■grows up between the cell-rows of the developing neck (fig. 13), 

 and the primary neck cell is cut off (fig. 14), and later divides into 

 :two. When the neck is full-grown the ventral-canal cell is sepa- 

 rated from the egg cell. When the egg is mature, and before 

 fertilisation has taken place, the cells surrounding the egg are 

 .generally divided, so that a small-celled layer surrounds the 

 egg (fig. 20). 



Sometimes in Cyathea one or two cells break away on the 

 opening of the neck. 



The nucleus of the egg cell becomes very clear, and stains 

 little just before fertilisation, and the nucleolus rapidly decreases 

 .in size. 



Should an egg cell fail to be fertilised, the walls of the colls 

 : surrounding are rapidly cuticularised and turn brown. This 

 process prevents bacteria and fungi from penetrating the soft 

 walls round the egg (fig. 20). A similar cuticularisation takes 

 place in prothallia attacked by fungi. A straight row of cell- 

 walls becomes cuticularised, and the part invaded by the fungus 

 is thus cut off. 



Sporophyte. 

 Embryo. 



The embryo is closely similar to that of the Poly pod iacece. 

 Immediately after fertilisation the cells of the neck that are 

 near the venter grow closely together and cut off communication 

 with the outside. The oospore grows considerably before 

 dividing, the nucleus remaining clear and nucleolus beinsj evi- 

 dent. After the octants are formed, divisions become irregular, 

 and the oval form is soon lost. A large apical cell is early re- 

 cognisable in one of the cotyledonary octants, and this grows 

 and divides more rapidly than the rest. 



The stem quadrant shows little division for a time, and 

 when the first leaf is fully developed appears as a green lateral 

 protuberance on the leaf-base. The second leaf arises opposite 

 the first, and the third almost opposite the second. The root 

 is as in the Polypodiacere. The extent of foot-formation de- 

 pends largely on the thickness of the prothallium. The octants 

 th it give rise to stem, leaf, and root are not in the same 

 plane. 



Th ■ first wall in the embryo is at right angles to the plane 



of the thallus, and the half nearest the apex of the thallus 



becomes stem and leaf; and this is the besl disposition 



■of the primary organs, whether the thallus is horizontal or 



vertical. 



i 



