“ Levi Cooke, of the District of Columbia, be, and he is hereby, appointed a commissioner to take and return the testimony in these causes, with the powers of a master in chancery, as provided in the rules of this court; but said commissioner shall not make any findings of fact or state any conclusions of law. ”

“ Provided, however, that if complainants shall conclude the taking of their evidence in chief before the 1st day of October, 1920, and shall give notice thereof, the time for the taking of evidence in chief on the part of defendant shall begin to run 15 days after the giving of said notice by the complainants ”