The Collaborative International Dictionary of English v.0.48:

Oosphere \O"o*sphere\ ([=o]"[-o]*sf[=e]r), n. [Gr. w,'o`n an egg
   + E. sphere.]
   [1913 Webster]
   1. (Bot.) An unfertilized, rounded mass of protoplasm,
      produced in an oogonium.
      [1913 Webster]

   Note: After being fertilized by the access of antherozoids it
         becomes covered with a cell wall and develops into an
         oospore, which may grow into a new plant like the
         parent.
         [1913 Webster]

   2. (Bot.) An analogous mass of protoplasm in the ovule of a
      flowering plant; an embryonic vesicle. --Goodale.
      [1913 Webster]

WordNet (r) 3.0 (2006):

oosphere
    n 1: a gamete; used especially of lower plants