FEMNS 343 



dots is enlarged at <. It is made up of a shield- 

 shaped scale covering a colony of sporangia. One 

 of the sporangia is much enlarged at e, and it 

 contains many spores. The dot t is known as a 

 f rait- dot or sorus (plural sori), and the shield- 

 like scale is an indiisium. In the maidenhair, the 

 sori are marginal, and the reflexed edge of the 

 frond forms the indusium. 



426. The so-called sensitive fern, which is very 

 common in low grounds, is illustrated in Fig. 359. 

 At the right is a leafy or sterile frond, and at 

 A a fertile frond. This fertile frond has the same 

 fundamental plan or structure as 

 the other one has, but the edges 

 of the lobes or divisions are 

 rolled backwards and form a 

 covering for the indusia and s6ri. 

 Here, then, are three general types 

 of fruit- bearing, — those in which 

 the edge of the frond serves as fig. 358. 



indusium, those having a scale-like Fructification of a shield - 



indusium, and those having a 

 scale -like indusium but the sori covered by the 

 revolute margins of the contracted frond. In 

 many ferns the sori are naked; that is, there 

 are no indusia. There are other types, but they 

 need not be discussed here. The best way to see 

 the spores of ferns is to press a ripe fruiting 



