  A matroid is sticky if any two of its extensions by disjoint sets can be
glued together along the common restriction (that is, they have an amalgam).
The sticky matroid conjecture asserts that a matroid is sticky if and only if
it is modular. Poljak and Turzik proved that no rank-3 matroid having two
disjoint lines is sticky. We show that, for r at least 3, no rank-r matroid
having two disjoint hyperplanes is sticky. These and earlier results show that
the sticky matroid conjecture for finite matroids would follow from a positive
resolution of the rank-4 case of a conjecture of Kantor.
