The Collaborative International Dictionary of English v.0.48:

Assimilatory \As*sim"i*la*to*ry\, a.
   Tending to assimilate, or produce assimilation; as,
   assimilatory organs.
   [1913 Webster]

WordNet (r) 3.0 (2006):

assimilatory
    adj 1: capable of taking (gas, light, or liquids) into a
           solution; "an assimilative substance [syn:
           assimilating, assimilative, assimilatory]