Locomotor Movements

in plants, the active movements in water characteristic of bacteria, lower algae, and Myx-omycetes, as well as of zoospores and spermatozoids.

Locomotor movements are caused by the unilateral action of directive stimuli (toward or away from them), such as light (phototaxis) and chemical substances (chemotaxis). In most cases, movement is effected by means of flagella (flagellate algae, bacteria, the zoospores of sessile algae and lower fungi, and the spermatozoids of algae, fungi, mosses, ferns, and some gymno-sperms) or, less commonly, by unilateral secretion of mucus (the green alga Closterium), active snakelike movements (the blue-green alga Oscillatoria, the sulfur bacterium Beggiatoa), unilateral movement of protoplasm (active diatomaceous algae), or formation of protoplasmatic excrescences (Myxomycetes).

Plants have evolved in the direction of losing their locomotor movements. Only bacteria, some algae, and Myxomycetes are motile in the vegetative state. In the other algae and in lower fungi, locomotor movements are characteristic only of zoospores and spermatozoids; in higher plants (mosses, club mosses, horsetails, ferns, sago palms, and ginkgo) only the spermatozoids are motile.