500 BOTANICAL GAZETTE [JUNE 
group. In several other genera the archegonia are borne in a 
terminal cluster, notably Grimaldia, Reboulia, and Clevea. This 
narrows the situation down to a single character common to these 
two genera (Targionia and Cyathodium) and not found in others. 
This is the common involucre inclosing the terminal group of 
archegonia. 
One glance at the diagrams will show how widely the two genera 
differ in all other respects save this. Targionia has perhaps as 
complex a thallus as is found in the entire group of Marchantiales; 
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5 5 
‘ VSL aN ge NO ES 
ee Oy 
3 : 2 
1 i 
Targionia Targionia 
oe ee ee Oe, Eee ea ee Ee 
5 5 
4 eee, / : ee 
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Cyathodium Targionia and Cyathodium 
Fic. 13.—Diagrams comparing Targionia and Cyathodium 
Cyathodium has perhaps the simplest, both as regards structure and 
the amount and character of differentiation. The thallus of 
Cyathodium consists of a simple ribbon, two layers of cells thick, 
the two layers slightly separated to form an air space, the air pores 
being simple openings in the upper layer of cells. 
In Targionia the antheridia are borne on a special portion of a 
special branch; in Cyathodium they are scattered in clusters along 
the edge of the thallus. In Targionia the foot and seta of the 
sporophyte are massive and well differentiated; in Cyathodium 
both foot and seta are represented by a single filament, four cells 
in length. 
In Targionia the elaters are true elaters, long pointed, and 
spirally banded; in Cyathodium the elaters, while spirally banded, 
are little more than dead nurse cells, short and stumpy. 
In but one character is Targionia less advanced than 
Cyathodium, and that is in the differentiation of the capsule wall 
