VITTARIA LINEATA i 208 
and a fifth central tetrahedral spore mother cell (f. 130, 136d). 
The cells which are to form the annulus divide by parallel walls 
into 13-15 cells (f. 737) which extend from the stalk at the base 
of the sporangium over the back a short distance down the other 
side, where they join with the thin-walled cells which connect 
with the lip cells (f. 7336). When the sporangium is young, 
these cells have thin walls and become inflated and raised above 
the other cells (f. 733a). These cells contain chlorophyl which 
is often retained until the spores are fully formed. 
As the sporangium ripens, the walls of the annulus thicken 
considerably with the exception of the dorsal wall, becoming 
cuticularized (f. 7344) and take on a golden brown color 
which later turns to a dull brown. The dorsal walls turn a dull 
yellow, and frequently bend back toward the inner walls of the 
cells, so that the cross walls form ridges along the annulus of the 
old sporangium. The other cells of the sporangium also divide. 
The frontal cells are generally eight in number and extend from 
the annulus to the pedicel at the base of the sporangium. They 
are composed of two kinds of cells, those whose walls do not 
thicken to any extent—called connective cells—and those whose 
walls thicken considerably forming the lips. There are four 
lip cells and they occupy the center of the row of seven or 
eight, occasionally nine (f. 233c, I 34c) These lip cells differ 
greatly from the other cells of the sporangium, having a short 
longitudinal diameter and a very long radial one. They are con- 
nected with the annulus by one to three thinner walled cells, 
and with the pedicel by two (/. 13366, 13400). The two lip 
cells, which occupy the center of the group of four, frequently 
thicken their walls to a greater extent than the other two, and it 
is between these two cells that the sporangium opens when the 
spores are ripe ( f. 754), the slit extending back generally in a 
straight line through the thin walls of the other cells almost to 
the annulus. The central tetrahedral cell of the sporangium 
divides by oblique walls until another tetrahedral cell has been 
formed inside of it (f. 730 gf), this inner cell dividing up into 
the spore mother cells and the cells between this cell and those 
constituting the sporangial wall form the tapetal cells ) 130, 
98), which dissolve after a time so that the spore mother cells 
