Biv OPAYTA ott 
is embedded in the tissue of the special upright branch of the 
thallus. When a spore germinates, it gives rise to a thallus 
producing archegonia and antheridia. 
The Marchantiales are generally considered to be closely related 
to the Ricciales. The gametophytes of this order are the most 



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Fic. 416. A group of antheridia of 
Anthoceros 
Fire. 415. Thallus of Anthoceros 
with six young unopened sporo- 
phy tes and two one sporophytes Each antheridium consists of a stalk, a 
which have split and show the covering of sterile cells, and many sperm 
columellae in the center. (x 14 cells. (x 215) 
highly specialized among the Hepaticae and are very different 
from those found in any other group of plants. From this it 
would appear that the Marchantiales represent a special line of 
evolution in which there has been a considerable development of 
the gametophyte. 
ORDER JUNGERMANNIALES 
Some of the members of this order have a simple thallus 
(Fig. 412), but in most cases the thallus is differentiated into 
stems and leaves (Fig. 413). The stems do not show a dif- 
ferentiation of tissues and have no specialized conducting cells. 
A leaf consists of a single layer of cells without a midrib. The 
