20 
PHARMACEUTICAL BOTANY 
Rupture of Sporangium and Spore Dissemination. — As was pre- 
viously indicated, each sporangial head has a row of cells with 
U-shaped thickenings around the margin called an annulus. As the 
sporangium matures the water escapes from the cells, pulling them 
together and holding the annulus like a bent spring. The thinner 
walled cells at the side of the spore case opposite the annulus, unable 
to stand the strain are consequently torn, the annulus straightens 
and a wide rent is made in the sporangium. The annulus then recoils 
and hurls the spores out of the sporangium. This closes the sporo- 
phyte generation. 
Fig. 3. — Sporangia of an undetermined species of fern; li, lip-cells; an, annulus; 
st, stalk; sp, mature spores. Each of the four nuclei in the upper cells of the 
stalk is in the terminal cell of one of the four rows of cells that compose the stalk. 
(Gager.) 
History of the Gametophyte or Sexual Generation. — The fern 
spore, falling upon a moist surface, germinates, producing a delicate 
green septate filament called a protonema. One end of this structure 
shows larger cells which, by the formation of oblique walls, cut out 
an apical cell of somewhat triangular shape. This is the growing 
point of what eventually becomes a mature green heart-shaped body 
called the “prothallium” or “prothallus.” The prothallium, about 
the size of an infant’s finger nail, develops on its under surface anther- 
idia, or male sexual organs, archegonia, or female sexual organs, and 
rhizoids or hair-like absorptive structures. The antheridia appear 
three to five weeks after spore germination. They are hemispherical 
in shape and are situated among the rhizoids toward the posterior 
end. Each antheridium consists of a three-celled wall which com- 
pletely surrounds the spermatocytes or mother-cells of the sper- 
matozoids. Within each spermatocyte the protoplasm arranges itself 
