Inherited FK Indexing

I have the following table set up:

CREATE TABLE states
(
   state_id integer NOT NULL DEFAULT nextval
('state_province_id_seq'::regclass),
   state character(2),
   full_name character varying,
   timezone character varying,
   CONSTRAINT "PK_state_id" PRIMARY KEY (state_id)
)

CREATE TABLE canadian_provinces
(
-- Inherited:   state_id integer NOT NULL DEFAULT nextval
('state_province_id_seq'::regclass),
-- Inherited:   state character(2),
-- Inherited:   full_name character varying,
-- Inherited:   timezone character varying,
   CONSTRAINT "PK_province_id" PRIMARY KEY (state_id)
)

as expected I can do select * from states and get everything out of
the child table as well.  What I can't do is create a FK to the
states table and have it look in the child table as well.  Is this on
purpose?  Is it possible to have  FK that spans into child tables?

Thanks