262 BRYOPHYTA 
habit, surrounded as it is up to full maturity by the tissues of the parent 
thallus. But the larger sporogonia of the Marchantiaceae project at 
maturity from their envelopes, and even during development their relation 
to the parent thallus is not uniform all round, their nutrition emanating 
mainly from base of the archegonium: a certain degree of polarity, 
expressed in the formation of a sterile foot for nutritive and mechanical 
purposes, is thus intelligible. ; 
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Fic. 122 
Monoclea Forsteri, Hook. 47=part of a longitudinal section of a capsule showing 
elaters and rows of spore-mother-cells. 350. 48=longitudinal section of the tip of a 
nearly mature capsule, showing the lobed spore-mother-cells. x160. 49=elaters, tetrads 
of spores, and a cell from the wall of a still more mature capsule. X350. (After Johnson.) 
But much more interest attaches to the internal differentiation of the 
capsule. The wall is initiated at a relatively early stage, and remains a 
single layer, excepting at the extreme apex: the mass of tissue which lies 
within, corresponding as it does in position to the sporogenous cells of 
iccia, is composed of cells all alike in origin, and it is often designated 
the archesporium (Fig. 121 1v.). But they do not all develop as spore- 
mother-cells: some become elongated, and form the well-known sterile 
elaters (Fig. 121 v. e2); others, undergoing more numerous divisions, 
remain fertile, and divide into spore-tetrads: a later stage of this differ- 
entiation is well illustrated in Fig. 122 for A/onoclea, a genus of doubtful 
