102 A TEXT-BOOk OF BOTANY 
divisivn of work occurs in the royal fern, climbing fern, 
ostrich fern, sensitive fern, moonwort (Fig. 184), adder’s 
tongue, etc. 
The sporangium of an ordinary fern consists of a spore- 
case with a slender stalk (ig. 185). The case has a del- 
icate wall formed of a single layer of cells; 
and, extending around it from the stalk and 
nearly to the stalk again, like a meridian 
line about a globe, is a row of peculiar cells 
185.—Section through the sorus of a shield fern, showing in- 
dusium and sporangia.—After ENGLER and PRANTL. 
with thick walls, forming a heavy ring. 
This ring is like a bent spring; and when 
the delicate wall begins to yield, the spring 
straightens violently, the wall is torn, and 
F1c.184.—A moon. 2* the spring rebounds the spores are hurled 
wort, showing With considerable force, like a handful of 
foliage and SP pebbles thrown forward from the hand. 
rangium -bearing 
ee ga ates This discharge of spores may be seen by 
Ba er MPTRAS- 6 4 % 
RURGER. placing some mature sporangia upon a moist 
