PTERIDOPHYTA 391 

Fig. 435. Archegonia of a fern 
Left, the neck-canal cells and ventral-canal cell are disorganized, but the arche- 
gonium has not opened ; right, archegonium open. (Redrawn after Strasburger) 

Fig. 436. Prothallus of a fern with young sporophyte attached 
Left, as seen from above ; right, as seen from below. (x 33) 
neck-canal cells become disorganized (Figs. 434, 485) and the tip 
of the archegonium opens (Fig. 435), so that there is a passage 
through which the sperm can reach the egg. The rounded basal 
part of the archegonium is sunk within the prothallus, while 
