  Coronal holes are well accepted to be source regions of the fast solar wind.
As one of the common structures in coronal holes, coronal plumes might
contribute to the origin of the nascent solar wind. To estimate the
contribution of coronal plumes to the nascent solar wind, we make the first
attempt to estimate their populations in solar polar coronal holes. By
comparing the observations viewed from two different angles taken by the twin
satellites of STEREO and the results of Monte Carlo simulations, we estimate
about 16--27 plumes rooted in an area of $4\times10^4$ arcsec$^2$ of the polar
coronal holes near the solar minimum, which occupy about 2--3.4% of the area.
Based on these values, the contribution of coronal plumes to the nascent solar
wind has also been discussed. A further investigation indicates that more
precise number of coronal plumes can be worked out with observations from three
or more viewing angles.
