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O14 Structural and Physiological Botany. © 
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most Ferns the sporangia are provided with an elastic ring, 
the annulus, running over the apex, which [by its contrac-. ; 
tion| causes the sporangium to burst [to allow the escape of 
the spores] (Fig. 440 1.); less often it surrounds the sporan- 
UGLY, 
LU, 
GU. 
wall 
Fic. 440.—Sporangia of = Fic. 441.—Reproduction of a Fern, Pfreris serrulata; I. 
Ferns; I. Aspfzdium with the prothallium proceeding from the spore; @ spore, 6 
vertical annulus: II, rhizoids, x y antheridia(x 80); II. an archegonium near 
Trichomanes with hori- the period of opening, @ central cell (x 400); III. the 
zontal annulus ; III. Os- young plant springing from the cordate prothallium ; w 
munda regalis, royal first leaf, ~ first root (natural size). 
fern, with incomplete 
annulus (all greatly magnified). 
* ‘ 
gium in a horizontal or oblique direction (Fig. 440 11. Tl). ~ ; = 
