348 PRACTICAL COURSE IN BOTANY 
(toward the margin), or the lower (toward the midrib). 
Look for a delicate membrane (indusiwm) covering the sori, 
and observe its shape and mode of attachment. If the 
specimen under examination 
is a polypodium, there will be 
no indusium; if a maiden- 
hair, or a bracken, it will be 
formed of the revolute mar- 
gin of the pinna. In lady 
fern and Christmas fern (As- 
495 496 pidium), the sori frequently 
Fies. 495-496.— Christmas fern (As- become confluent, that is, so 
pidium): 495, part of a fertile frond, natural 
size; 496, a pinna enlarged, showing the close together as to appear 
sori confluent under the peltate indusia. like a solid mass. Sketch a 
fertile pinna as it appears under the lens, bringing out all 
the points noted. 
405. The spore cases. — Look under the indusium at 
the cluster of little stalked circular. appendages (Fig. 490). 
These are the sporangia, or spore cases, in which the re- 
productive bodies are borne. Place one of them under the 
microscope, and it will be found to consist of a little stalked 
circular body like a tennis racket (Fig. 491), surrounded 
by a jointed ring 
called the an- 
nulus. Watch a 
few moments and 
see if you can 
find out the use Fies. 497-500. — Spores of pteridophytes, magnified: 
of the annulus. 497, a fern spore ; 498, 499, two views of a spore of a club 
If not, warm the moss ; 500, spore of a common horsetail (Equisetum arveuse). 
slide and you will probably see the ring straighten itself 
with a sudden jerk, rupturing the wall of the sporangium 
and discharging the spores with considerable force. If this 
does not happen, add a drop of strong glycerine to a speci- 
men mounted in water; the rupture will be apt to follow 
quickly. What causes it, in either case? [56, (1); Exp. 19.] 
497 498 499 500 
