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