FILICALES 



345 



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

 normal life-cycle cannot be completed without it. ,} 



Fig. 286. 

 Fertilisation in Onoclea sensibilis : the arrows indicate direction to tlic growing 

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

 after entrance of the first sperinatozoid. ( x 500.) i? = vertical section of the venter 

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

 tozoid within the nucleus. Thirty minutes. ( x 1200.) (After Shaw.) 



The immediate consequence of fertilisation is growth and segmenta- 

 tion of the zygote, which flrst secretes a cell-wall. Jt divides into 



m 



x«-;; 





Fig. 287. 



Horizontal section of an egg, showing coiled male nucleus within the fcmal.-. Twrlvr 



hours. ( X 1200.) (.\fter Shaw.) 



octants, four of which constitute an epibasal hemisphere, directed 

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



