involucrum

Involucrum \In`vo*lu"crum\, n.; pl. L. {Involucra}, E.
   {Involucrums}. [L. See {Involucre}.]
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   1. (Bot.) See {Involucre}.
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   2. (Zool.) A sheath which surrounds the base of the lasso
      cells in the {Siphonophora}.
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Involucre \In"vo*lu`cre\ (?; 277), n. [L. involucrum a covering,
   wrapper, fr. involvere to wrap up, envelop: cf. F. involucre.
   See {Involve}.] (Bot.)
   (a) A whorl or set of bracts around a flower, umbel, or head.
   (b) A continuous marginal covering of sporangia, in certain
       ferns, as in the common brake, or the cup-shaped
       processes of the filmy ferns.
   (c) The peridium or volva of certain fungi. Called also
       {involucrum}.
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