348 



PRACTICAL COURSE IN BOTANY 



495 490 



Figs. 495-496. — Christmas fern (As- 

 pidium) : 495, part of a fertile frond, natural 

 size ; 496, a pinna enlarged, showing the 

 sori confluent under the peltate indusia. 



(toward the margin), or the lower (toward the midrib). 

 Look for a delicate membrane iindusium) 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 re volute mar- 

 gin of the pinna. In lady 

 fern and Christmas fern {As- 

 indium), the sori frequently 

 become confluent, that is, so 

 close together as to appear 

 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 

 of the annulus. 

 If not, warm the 

 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 



Figs. 497-500. — Spores of pteridophytes, magnified : 

 497, a fern spore ; 498, 499, two %aews of a spore of a club 

 moss ; 500, spore of a common horsetail (Equisetum arveuse) . 



