PERNS. 



171 





in Polypody. Observe, then, that in Polypody the sori are not 

 covered, whilst in Pteris the opposite is the case. The covering 

 of the fruit-dots is technically known as the indusium. The 

 individual spore-cases are alike in both plants. 



Fig. 204: shows a frond of one of our commonest Shield-Ferns 

 (Aspidium acrostichoides). It is simply pinnate. The stipe is 

 thickly beset with rusty -look ing, chaff-like scales. The veins 

 are free, as before. The sori or fruit-dots 

 are on the back of the upper pinnae, but 

 they are neither collected in naked clus- 

 ters, as in Polypody, nor are they covered 

 by the edge of the frond as in the Brake. 

 Here each cluster has an indusium of 

 its own. The indusium is round, and 

 attached to the frond by its depressed 

 centre (peltate). Fig. 265 shows an en- 

 larged portion of a pinna, with the sporan- 

 gia escaping from beneath the indusium. 

 From one forking vein the sporangia are 

 stripped off to show where they have 

 been attached. The separate sporangia 

 discharge their spores in the manner 

 represented in the account of Polypody. 

 In some Ferns the fruit-dots are elong- 

 ated instead of being round, and the 

 indusium is attached to the frond by 

 one edge only, being free 

 on the other. Sometimes 

 two long fruit-dots will be 

 found side by side, the 

 free edges of the indusia 

 being towards each other, 

 so that there is the appearance of one 

 long fruit-dot with an indusium split 

 down the centre. 



Fig. 266 represents a frond of a very 

 Fig. 26*. common swamp Fern, Onoclea Sensibilis, 

 or Sensitive Fern. It is deeply pinnatifid, and on one of the 



Fig. 265. 



