  The plasmodium of Physarum polycephalum is renowned for spanning sources of
nutrients with networks of protoplasmic tubes. The networks transport nutrients
and metabolites across the plasmodium's body. To imitate a hypothetical
colonisation of the world and formation of major transportation routes we cut
continents from agar plates arranged in Petri dishes or on the surface of a
three-dimensional globe, represent positions of selected metropolitan areas
with oat flakes and inoculate the plasmodium in one of the metropolitan areas.
The plasmodium propagates towards the sources of nutrients, spans them with its
network of protoplasmic tubes and even crosses bare substrate between the
continents. From the laboratory experiments we derive weighted Physarum graphs,
analyse their structure, compare them with the basic proximity graphs and
generalised graphs derived from the Silk Road and the Asia Highway networks.
