  We analyze the filamentarity in the Las Campanas redshift survey (LCRS) and
determine the length scale at which filaments are statistically significant.
The largest length-scale at which filaments are statistically significant, real
objects, is between 70 to $80 h^{-1}$Mpc, for the LCRS $-3^o$ slice.
Filamentary features longer than $80 h^{-1}$Mpc, though identified, are not
statistically significant; they arise from chance alignments. For the five
other LCRS slices, filaments of lengths $50 h^{-1}$Mpc to $70 h^{-1}$Mpc are
statistically significant, but not beyond. These results indicate that while
individual filaments up to $80 h^{-1}$Mpc are statistically significant, the
impression of structure on larger scales is a visual effect. On scales larger
than $80 h^{-1}$Mpc the filaments interconnect by statistical chance to form
the filament-void network. The reality of the $80 h^{-1}$Mpc features in the
$-3^o$ slice make them the longest coherent features in the LCRS. While
filaments are a natural outcome of gravitational instability, any numerical
model attempting to describe the formation of large scale structure in the
universe must produce coherent structures on scales that match these
observations.
