FILICALES 



345 



of external fluid water is essential for fertilisation in Ferns. Their 

 normal life-cycle cannot be completed without it. _^ 



Fig. 2S6. 

 Feililisation in Onoclca sensibilis : the arrows indicate direction to^'the gro^Tng 

 point. A =3. vertical section through an archegonium probably within ten minutes 

 after entrance of the first spennatozoid. ( x 500.) £ =vertical section of the venter 

 of an archegonium, containing spermatozoids, and the collapsed egg with a sperma- 

 tozoid within the nucleus. Thirtj' minutes. ( x 1200.) {After Shaw.) 



The immediate consequence of fertilisation is growth and segmenta- 

 tion of the zygote, which first secretes a cell-wall. It divides into 



Fig. 2S;. 



Horizontal section of an egg, showing coiled male nucleus within the female. Twelve 



hours. { X 1200.} {.-Vfter Shaw.) 



octants, four of which constitute an epihasal hemisphere, directed 

 towards the apex of the parent thallus, giving rise to axis and leaf oi 



