D.C. Code § 10-153
The authority of the commission created by § 10-152 is extended to include the acquisition of such additional lands and premises lying adjacent to or in the immediate vicinity of the taking lines as shown on the map on file in the Office of the Executive and Disbursing Officer and known as the map of the Rock Creek and Potomac Parkway (in 4 sheets) dated May, 1923, as may in its discretion, subject to the approval of the Commission on the Arts and Humanities, be necessary for the best development of the connecting parkway between Rock Creek Park, the Zoological Park, and Potomac Park; provided, that the total sum expended for lands needed for this parkway shall not exceed that authorized by § 10-152, and amended by the Second Deficiency Act of May 5, 1926; provided further, that the commission may exclude such lands and premises, not owned by the United States on March 2, 1929, but within the taking lines heretofore authorized for the said Parkway, as may in its discretion, and upon the advice of the Commission on the Arts and Humanities, be found not to be desirable or necessary for the connecting parkway.
D.C. Code § 10-153