A combine harvester (10) comprises threshing and separating apparatus (12,14) which are arranged to process a cut crop stream and each comprising a grate arrangement through which material separated from the crop stream falls under gravity. Grain conveyance means (16) arranged below the threshing and separating apparatus (12,14) catch the falling grain and material other than grain (MOG). A stratification pan (26) is located below a front region of the threshing and separating apparatus (12,14) and a return conveyor (28) is located below a rear region of the threshing and separating apparatus, both conveyors (26,28) being driven in a oscillating manner. The return conveyor (28) conveys said grain and MOG in a forward direction to a front edge (28F) thereof which is located above the stratification pan (26). The stratification pan (26) conveys collected material rearwardly to a rear edge (26R) from where the collected material falls under gravity into a cleaning unit (20). An accelerator roller (36) is provided and is rotateably driven on a transverse axis in front of the front edge (28F) of the return conveyor (28). Material caught by the return conveyor (28) is incident upon the accelerator roller (36) and paddles (38) provided on the accelerator roller (36) serve to accelerate the material from the return conveyor (28) forwardly.La présente invention concerne une moissonneuse-batteuse (10) qui comprend des appareils de battage et de séparation (12, 14) qui sont conçus pour traiter un flux de récolte coupée, chacun comprenant un système de grille à travers lequel le matériau séparé à partir du flux de récolte tombe sous leffet de la gravité. Le moyen de transport de céréale (16) est disposé en dessous de lappareil de battage et de séparation (12, 14) attrape le grain et le matériau autre que le grain (MOG) qui tombent. Un bac de stratification (26) est situé au-dessous dune région avant de lappareil de battage et de séparation (12, 14) et un convoyeur de retour (28
