The Collaborative International Dictionary of English v.0.48:

Heterogamy \Het`er*og"a*my\, n. [See Heterogamous.]
   [1913 Webster]
   1. (Bot.) The process of fertilization in plants by an
      indirect or circuitous method; -- opposed to orthogamy.
      [1913 Webster]

   2. (Biol.) That form of alternate generation in which two
      kinds of sexual generation, or a sexual and a
      parthenogenetic generation, alternate; -- in distinction
      from metagenesis, where sexual and asexual generations
      alternate. --Claus & Sedgwick.
      [1913 Webster]