Source : Webster's Revised Unabridged Dictionary (1913)

Indusium \In*du"si*um\, n.; pl. {Indusia} (-[.a]). [L., an under
   garment, fr. induere to put on: cf. F. indusie the covering
   of the seed spots of ferns.] (Bot.)
   (a) A collection of hairs united so as to form a sort of cup,
       and inclosing the stigma of a flower.
   (b) The immediate covering of the fruit dots or sori in many
       ferns, usually a very thin scale attached by the middle
       or side to a veinlet.
   (c) A peculiar covering found in certain fungi.

Source : WordNet®

indusium
     n : a membrane enclosing and protecting the developing spores
         especially that covering the sori of a fern
     [also: {indusia} (pl)]

indusia
     See {indusium}