Where a power to dispose of lands is confined to a disposition by devise or will, the instrument of execution must be a will duly executed; and where a power is confined to a disposition by grant it cannot be executed by will, although the disposition is not intended to take effect until after the death of the party executing the power.
D.C. Code § 42-1018
Wills, see §§ 18-108, 18-303. .