zariski tangent spaces of schubert varieties

i've been writing a bit recently about invariant distributions on partial flag varieties and how this relates to singularities of schubert varieties and so forth. i want to try developing some of this a bit more systematically, in particular by trying to develop a systematic procedure for reading off from a root system the zariski tangent space of an arbitrary schubert variety at the "basepoint". or something like that...