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 Botrychium. 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 
f< $g HP 
"* 'V -*> >''/. ' ' ,', './ 
..-' ':- ':-- ' 
FIG. 158. Cross-section of the thallus of a hornwort (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- 
