The Collaborative International Dictionary of English v.0.48:

Perigone \Per"i*gone\, n. [Pref. peri- + Gr. ? productive
   organs.]
   1. (Bot.)
      (a) Any organ inclosing the essential organs of a flower;
          a perianth.
      (b) In mosses, the involucral bracts of a male flower.
          [1913 Webster]

   2. (Zool.) A sac which surrounds the generative bodies in the
      gonophore of a hydroid.
      [1913 Webster]

WordNet (r) 3.0 (2006):

perigone
    n 1: collective term for the outer parts of a flower consisting
         of the calyx and corolla and enclosing the stamens and
         pistils [syn: perianth, chlamys, floral envelope,
         perigone, perigonium]