FERNS. 



173 



which, much magnified, is shown in Fig. 268. You may. open 



out one of these little globes, and then you will have something 



like what is shown in an enlarged form in Fig. 269. It now looks 



more like a pinnule than when it was 



roiled up, and it now also displays the 



fruit-dots on the veins inside. Here, * 



then, we have evidently two kinds of 



frond. That bearing the fruit-dots we 



shall call the fertile frond, and the other 



we shall call the sterile one. You must 



not look upon the pinnule in which the 



sori are wrapped up as an mdusium. 



Sori which are wrapped up in this way 



have an indusium of their own besides, 



but in this plant it is so 



obscure as to be very 



difficult to observe. 



The spore-cases burst 

 open by means of an 

 elastic ring as before. 



Fig. 270 represents 

 one of the Moon- 

 worts (Botrychi- 

 urn \ r irginicum), 

 very common in- 

 our rich woods 

 everywhere. Here 

 we hive a single 

 frond, but made 

 up manifestly of 

 two distinct por- 

 tions, the lower 



sterile and the upper fertile. Both portions are 

 thrice-pinnate. The ultimate divisions of the 

 fertile segment are little globular bodies, but 

 you cannot unroll them as in the case of the 

 Onoclea. Fig. 271 shows a couple of them greatly enlarged. 

 There is a slit across the middle of each, and one of the slits is 



