DEVELOPMENT OF PLANTS 



285 



ever, are but modified branches of the thallus and bear the 

 sexual organs upon their upper surfaces in Hnes radiating from 

 the center of the branches. Fertilization is effected, as in all 

 forms, by means of dews and rains which flood these organs with 

 water. An examination of a young archegonial branch will show 

 how admirably it is constructed to ensure fertilization. The 

 archegonia radiating in lines have their necks strongly curved 



Fig. 191. Fig. 192. 



Fig. 191. Section of an archegonial branch similar to a, Fig. 190 — ar, 

 archegonia; in, involucre or curtain that hangs down on either side of the 

 rows of archegonia; ac, air chambers; th, thallus. 



Fig. 192. Section of a young antheridial branch: an, antheridia sunken 

 in cavities of the branch, which is also provided with air chambers similar 

 to those of the normal thallus. Some of the antheridia have discharged 

 their gametes, as at x. 



upwards and away from the center of the branch. These lines 

 of archegonia are separated by ridges which thus act as a water- 

 shed, deflecting into the upturned necks any water containing 

 gametes that may chance to fall upon them. After fertilization 

 these mushroom-shaped branches elongate, raising the sexual 

 organs up into the air, where the antheridial branch assumes the 

 form of a lobed disc, while the archegonial branch terminates in 

 an umbrella-like structure (Figs. 186, 190). Owing to the ex- 

 tended growth of this latter branch, the archegonia come to lie 

 on the under side of the structure between the finger-like out- 

 growths, where they are completely hidden and protected by 

 fringed curtains, the involucre, that hang down from the fingers. 



