t921] HAUPT—REBOULIA 65 
receptacle becomes lifted up on a stalk only after the sporophytes 
are approaching maturity. The archegonia appear in the autumn, 
fertilization occurs, and the embryo develops immediately. The ~ 
sporophyte, however, does not mature until the following spring. 
ANTHERIDIUM 
The antheridia occur in sessile lunate receptacles which are 
sometimes irregular in outline and broken up into several pieces. 
The receptacle is cushion-shaped and slightly raised above the 
general level of the thallus, but the antheridia themselves are 
rather deeply sunken in the main body of the thallus. Four, or 
occasionally 5, antheridia are usually seen in cross-section, and 
4-6 in longitudinal section, but often more, and in rare cases as 
many as 24 were counted in longitudinal section. The number 
of antheridia in a receptacle, therefore, varies from about 16 to 
Over I00. 
Usually 2 and rarely 3 groups of antheridia are produced 
successively on the thallus before the appearance of the archegonial 
receptacle. They are formed in rather close proximity (about 7-10 
cells removed) to the apical cell, and each group becomes isolated 
by a rather wide area of sterile tissue of the thallus. In all cases 
the antheridia develop strictly in acropetal succession from seg- 
ments of the apical cell. Air chambers are abundantly formed in 
the raised portion of the thallus which communicate with the surface 
by means of air pores similar to those which occur on the rest of 
the thallus. By growth of the epidermal cells around the pores 
which communicate with the antheridial cavities, a plate of cells 
is formed containing a small central perforation through which the 
sperms escape (fig. 3). 
he simplest arrangement of the antheridia among the Marchan- 
tioideae may be represented by Clevea, in which they are sunken in 
the back of the thallus and not arranged in groups. In Sauteria 
the antheridia occur in raised groups along the median line of the 
thallus. In Fimbriaria and Reboulia there is an intermittent 
development of antheridia, which occurs in raised groups without 
checking the activities of the apical cell. The situation is similar 
in Aytonia (Plagiochasma), except that the apical cell does not 
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