348 



PRACTICAL COURSE IN BOTANY 



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

 Look for a delicate membrane (indusium) 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- 

 pidium), the sori frequently 



495 



496 



FIGS. 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 ClOS6 together as to appear 

 sori confluent under the peltate indusia. 



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 



FIGS. 497-500. Spores of ptendophytes, magnified : 



Of the annuluS. 497, a fern spore ; 498, 499, two views of a spore of a club 

 If not Wfl rm t h P moss .' ^00, 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 



499 



500 



