  A root system $R$ of rank $n$ defines an $n$-dimensional smooth projective
toric variety $X(R)$ associated with its fan of Weyl chambers. We give a simple
description of the functor of $X(R)$ in terms of the root system $R$ and apply
this result in the case of root systems of type $A$ to give a new proof of the
fact that the toric variety $X(A_n)$ is the fine moduli space $\bar{L}_{n+1}$
of stable $(n+1)$-pointed chains of projective lines investigated by Losev and
Manin.
