[en] A study of scaling violations in fragmentation functions is presented. ALEPH data samples enriched in b jets, u, d, s jets and gluon jets, respectively, together with measurements of the longitudinal and transverse inclusive cross sections, are used to extract the fragmentation functions for each flavour. Comparing these measurements to lower energy data (PEP, PETRA and TRISTAN), scaling violations consistent with QCD are observed and a measurement of the strong coupling constant α_s(M_Z²)=0.127±0.011 is obtained. ((orig.))