The basis for determining the gain or loss from the sale or other disposition of property acquired before March 1, 1913 shall be: (1) the cost of such property (or, in the case of such property as is described in subsection (a) * * * (5) * * * of this section, the basis as therein provided), or (2) the fair market value of such property as of March 1, 1913, whichever is greater.'