214 



STRUCTURE AND LIFE HISTORIES 



their location and mode of origin, the antheridia of some 

 of the lower, or eusporangiate, ferns, such as Ophioglosum 

 and BotrycJiium. The archegonia are also imbedded, with 

 the tip of the neck reaching to the surface (Fig. 159). 

 They are further concealed at maturity by the growth of 



Fig. 158. — Cross-section of the thallus of a horn wort (Anthoceras sp.). 

 The oval area is an antheridium, containing sperms, or sperm-mother- 

 cells. 



Fig. 159. — Anthoceros fusiformis. Vertical longitudinal section near 

 the apex of the thallus, showing archegonia (at the left), and antheridia 

 (at the right). X about 53. (After M. A. Howe.) 



a small dome of tissue over the opening where the neck 

 comes to the surface. Both antheridia and archegonia 

 occur on the same plant, sometimes closely intermingled. 

 196. Symbiosis. — A most interesting case of symbiosis 

 occurs between Anthoceros and a much more lowly organ- 



