  The influence of the gravitational field on the reversible process of
assembly and disassembly of linear aggregates is focus of this paper. Even the
earth gravitational field can affect the equilibrium properties of heavy
biological aggregates such as microtubules or actin filaments. The gravity
gives rise to the concentration gradient which results in the distribution of
aggregates of different lengths with height. Strong enough gravitational field
induces the overall growth of the aggregates. The gravitational field
facilitates the isotropic to nematic phase transition reflecting in a broader
transition region. Coexisting phases have notedly different length
distributions and the phase transition represent the interplay between the
growth in the isotropic phase and the precipitation into nematic phase. The
fields in an ultracentrifuge can only reinforce the effect of gravity, so the
present description can be applied to a wider range of systems.
