A power lawn mower including a plastic endless chain type cutter assembly having a plurality of plastic whip sticks which produce aeration and suction within the mower casing for improving grass cutting and dispensing. Each whip stick includes an elongated generally flat portion which extends horizontally and merges with a main lift or curved wing portion with the wing portion including a leading impact edge and a trailing lift edge. In operation, the cutter assembly is moved continuously with the lift portions of the whip sticks acting to create an aerating effect for causing a vacuum or suction within the mower casing. This action causes a continuous flow of air to be drawn between the ground and casing for discharging cut grass outwardly through an opening in the casing. The whip sticks are permitted limited pivotal movement upon striking obstacles during rotation. The cutter assembly is supported during powered rotational movement on elongated horizontal portions of a chain guide and support member. A guard is mounted to the chain guide and support member, and the guard includes a slot along which the flat horizontal portions of the whip sticks move as they are being rotated. The guard and a portion of the mower casing form an enclosure or tunnel which permits efficient transferring of cut grass from the casing.