  Two aspects of filamentary molecular cloud evolution are addressed: (1)
Exploring analytically the role of the environment for the evolution of
filaments demonstrates that considering them in isolation (i.e. just addressing
the fragmentation stability) will result in unphysical conclusions about the
filament's properties. Accretion can also explain the observed decorrelation
between FWHM and peak column density. (2) Free-fall accretion onto finite
filaments can lead to the characteristic "fans" of infrared-dark clouds around
star-forming regions. The fans may form due to tidal forces mostly arising at
the ends of the filaments, consistent with numerical models and earlier
analytical studies.
