ON GENERA AND SPECIES. 19 
_ Accessory indusia are formed of the entire margin of the 
frond, or a portion of it being changed in texture and form 
and inflexed, its margin conniving with the free margin 
of the interiorly attached special indusium, the two thus 
combined forming a continuous or interrupted groove, 
opening exteriorly. When the special indusium is pro- 
duced on a punctiform receptacle, an wrceolate, bilabiate, or 
tubular cyst is formed, which contains the sporangia, some 
being exerted beyond the margin (pedicellate); while in 
some cases the cyst is antemarginal, and is then termed 
cucullate, in all these cases opening exteriorly, but often 
more or less turned inwards, and then having the appearance 
of being on the under side of the margin. | 
am Universal indusia occurs when the segments of the fertile 
Ge fronds are contracted. They consist of the margins of the 
_ Segments being more or less changed in texture, becoming — : : : 
. membranous, and folded inwards (involute*), the two ` p 
| Opposite margins generally meeting, and thus enclosing all 
~ the sori upon the segment, whatever may be their form or ` 
c position upon the veins, the segments thus assuming the 
form of a pod or siliqua. (sliquiform) as in. Struthiopteris ; 
or of a berry (bacciform) as in Onoclea. 
... Tn some Polypodec the sori are furnished with scales of 
various forms; in Pleopeltis they consist of numerous 
Orbieular peltate scales, imbricate over one another, and 
covering the sporangia of each sori; in Hymenolepis they 
are very thin and membranous ; in Lopholepis they consist 
Schellolepis they are irregularly laciniated ; club like and 
ther forms are also common to the genera Vittaria and 
Tonitis, Such bodies are considered to be imperfect 
one > another on the under side of the frond or — 
of numerous slender scales, longer than the sporangia; in a 
* "That is, the margins turned or rolled inwards, so as to face and o 
