of fig1 fig1 is a fragmentary sectional view taken substantially as indicated along the line xiv xiv of fig1 and fig1 is a fragmentary sectional view taken substantially as indicated along the line xv xv of fig1 referring first to fig1 of the drawings the apparatus of the present invention is illustrated as applied to a tree harvester of the kind disclosed in u s pat no 4 108 224 owned by applicant 39 s assignee a tracktype vehicle indicated generally at 20 includes a frame 21 upon which a boom beam hereinafter usually termed a 34 boom 34 22 is pivotally mounted and a hydraulic cylinder 23 permits an operator to selectively raise and lower the boom pivoted on the free end of the boom 22 is an arm beam hereinafter generally called an 34 arm 34 24 which is movable about its pivotal connection on the boom 22 by means of a hydraulic cylinder 25 pivotally mounted at the free end of the arm 24 is a tree harvesting mechanism indicated generally at 26 the angular aspect of which relative to the arm 24 is controlled by a hydraulic cylinder 27 the tree harvesting mechanism 26 has various hydraulically operated components such for example as a shear 28 operated by cylinder 28a a tiltable frame 29 controlled by a hydraulic cylinder 30.