MOSSES AND LIVERWORTS 113 
The spores arise from a single subepidermal layer 
of cells (Fig. 28, D), which later becomes deeper 
seated through the further division of the superficial 
cells (EZ). Within the sporogenous layer, or arche- 
sporium, is a central cylinder of sterile cells forming 
the “columella,” which both in origin and position 
seems to represent the axial vascular bundle or strand 
of conducting cells found in the young sporophyte of 
the ferns, and it is not impossible that it may also serve 
as a conducting tissue, thus representing a primitive 
vascular bundle physiologically as well as structurally. 
Owing to the absence of a root connecting the sporo- 
phyte with the earth, it remains dependent upon the 
gametophyte for its supply of water and also for cer- 
tain food elements, and if the gametophyte perishes, the 
sporophyte necessarily soon dies as the supply of water 
is cut off. Otherwise, owing to the perfect assimilative 
system, it is quite independent, and if a root were pres- 
ent would be entirely so. 
Tur True Mosszes (Muse?) 
The second class of the Bryophytes, while greatly 
outnumbering the liverworts, shows very much less 
range of structure and is evidently a much more spe- 
cialized group. These “True Mosses,” with few ex- 
ceptions, show an almost stereotyped plan of structure, 
the differences between them being mostly of minor 
importance.. There are a few, however, notably the 
peat-mosses (Sphagnacez), which show affinities with 
the liverworts, especially with Anthoceros. 
The gametophyte of the Musci usually exhibits two 
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