What is "illegitimate fertilization"

Illegitimate \Il`le*git"i*mate\, a.

1. Not according to law; not regular or authorized; unlawful; improper.

2. Unlawfully begotten; born out of wedlock; bastard; as, an illegitimate child.

3. Not legitimately deduced or inferred; illogical; as, an illegitimate inference.

4. Not authorized by good usage; not genuine; spurious; as, an illegitimate word.

   Illegitimate fertilization, or Illegitimate union (Bot.), the fertilization of pistils by stamens not of their own length, in heterogonously dimorphic and trimorphic flowers.
   --Darwin.