  Electronic excitations in a graphitic monolayer (graphene) in the
long-wavelength approximation are characterized by the linear dispersion law,
representing a unique example of the really two-dimensional "ultrarelativistic"
fermionic system which in the presence of topological defects possesses rather
unusual properties. A disclination that rolls up a graphitic sheet into a
nanocone is described by a pointlike pseudomagnetic vortex at the apex of the
cone, and the flux of the vortex is related to the deficit angle of the conical
surface. A general theory of planar relativistic fermionic systems in the
singular vortex background is employed, and we derive the analytical expression
for the charge which is induced at finite temperature on some graphitic
nanocones.
