The Collaborative International Dictionary of English v.0.48:

Informatory \In*form"a*to*ry\, a.
   Full of, or conveying, information; instructive. [R.]
   --London Spectator.
   [1913 Webster]

WordNet (r) 3.0 (2006):

informatory
    adj 1: providing or conveying information [syn: informative,
           informatory] [ant: uninformative]