The Collaborative International Dictionary of English v.0.48:

Idorgan \Id*or"gan\, n. [Gr. ? form + E. organ.] (Biol.)
   A morphological unit, consisting of two or more plastids,
   which does not possess the positive character of the person
   or stock, in distinction from the physiological organ or
   biorgan. See Morphon. Idrialine