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128 BOTANICAL GAZETTE [AUGUST 
formed upon its inner surface. This is the exospore ( figs. 20-22). 
The spores increase in volume, but the exospore expands so 
much more rapidly than does the protoplasmic content, that 
the latter is left in the apical portion of the spore cavity asa | 
tenuous spherical vesicle of protoplasm filled with a limpid 
fluid (fig. 377). A single very small nucleus, in which with 
difficulty may be seen one or two nucleoli, lies in the region 
nearest the spore apex, _The rest of the spore cavity between _ 
the vesicle and the exospore is filled with a limpid fluid of the 
same nature as that which occupies the space between the tetrad 
and the mother cell membrane. Soon hair-like radiations appear 
traversing these fluid regions (figs. 42, 43), whose general 
direction is from the spore mother cell membrane toward the * “* 
center of the tetrad. A thick layer which stains very deeply | 
appears upon the inner face of the exospore (fig. 37). The i 
latter maintains its more rapid rate of growth and soon after- 
ward is widely separated from this layer, by a space filled plage 
with the liquid and the radial fibrillae (figs. 38,42). The 
sculpturing of the exospore begins almost immediately upon its ¢ 
inception. The spines are laid down by depositions of matter 
derived from the liquid between the teres ane and the — Pe 
cell membrane ( figs. 42-46). ~-#e ern 
As the megaspores increase rae size, “nef are fotsue i speek iy 
the liquid in which they float seeping in between them (figs. 35,» 4-<< 
42, 43) and the exospore is ruptured between the spores in such »¢« ee 
manner that each presents the appearance of a tetrahedron with a 4 
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hemispherical base and three plane triangular faces. The tearing 
apart of the spores leaves a trefoil-shaped cleft extending from 
the apex along the three ridges between the triangular faces, 
and bounded by the flaring flaps of the torn exospore ( fig. 58). 
The sterile mother cells in part disappear by dissolving in) 
the slimy fluid in the sporangium cavity, but not until the exo- ~~~ vie 
spore is well developed. Some persist however throughout the 7 
development of the gametophyte and perhaps may grow slightly; ie 
they never divide. ne 
FEMALE GAMETOPHYTE.—The spore is but a small fraction of 
