100 
MORPHOLOGY 
produce spores, is said to be sterile. This sterile tissue in Marchantia t 
which was sporogenous tissue in the Ricciaceae, forms a region of the 
sporophyte quite distinct from the spore-producing region, so that in the 
mature sporophyte three regions are recognized: 
(i) the capsule, containing the spores; (2) the 
seta, a short stalk beneath the capsule, which 
elongates rapidly as the capsule matures; and 
(3) the foot, a spreading structure in which the 
seta ends, and which anchors the sporophyte in 
the gametophyte and also acts as an absorbing 
organ (fig. 230). 
The spore production of Marchanlia is further 
diminished by the fact that not all the potentially 
sporogenous cells produce spores. Some of them 
become converted into curious elongated, fiber-like 
cells with spiral thickening (elaters}, which by their 
hygroscopic movements assist in loosening up the 
spore mass in connection with dehiscence and 
FIG. 230. Mar- scattering. The usual calyptra is formed about 
chantia: sporophyte, tne developing sporophyte by the venter of the 
showing capsule (con- , . , , 
taining spores and ela- archegomum, but at maturity the capsule breaks 
ters), seta, and foot through this by the rapid elongation of the seta, 
(embedded in tissue of After j ts escape f rom t h e calyptra the capsule 
gametophyte). , , 
breaks irregularly and discharges its spores. 
Conclusions. The Marchantiales are characterized by a distinct 
and strong differentiation of the tissues of the gametophyte, leading to 
the highly complex thallus of Marchanlia, with its specialized mechanism 
for photosynthesis. There is observable in the group also a distinct 
tendency in the sporophyte toward the sterilization of the potentially 
sporogenous tissue into the sterile tissue developing the seta and foot. 
This means that seta and foot are derived historically from sporogenous 
tissue. The development of the seta, moreover, is associated with the 
dispersal of spores, its rapid elongation freeing the capsule from the 
calyptra. The further sterilization of potentially sporogenous tissue in 
the production of elaters is another feature of the group, and is also 
associated with spore dispersal. On the whole, the chief distinction of 
Marchantiales as compared with the other groups of liverworts is the 
differentiation of the tissues of the gametophyte, which has reached its 
extreme expression in Marchantia. 
