LOCOMOTION (from Lat. locus, place + motio, motion, from ntovere, to move). In plants, the free spontaneous movements from place to place that occur in lower forms and in the so called zoospores of higher forms. Swimming movement occurs in many of the lower alga and fungi, in zoospores of higher algx, and in sperms of mosses and ferns. It is found as far up the scale of plant life as the gymnosperms, Ginkgo, Cycas, and Zamia, in which the male cells, which correspond physiologically to the sperms of low er forms, arc freely motile. A creeping (amce boid) movement over a moist surface occurs in the masses of naked protoplasm (plasmodia) which constitute the vegetative stage of slime molds. Swimming movements are usually due to the rapid lashing of long or short protoplasmic processes (cilia) which propel the organism through the water. They are very minute and often numerous, the entire surface of some zoospores (e.g. those of Vaucheria) being cov ered with them. Sometimes, however, there are four, three, two, or only one. In this case they are longer than when more numerous. A single large cilium is often termed a flagellum.
The mechanism of the movement of diatoms is not yet fully known. Some forms creep by means of protrusions of the protoplasm through the slit (raphe) which traverses the siliceous wall length wise. Amwboid movements are brought about by a flowing motion of the naked protoplasm which composes the organism. One or more processes
form on one side of the body and elongate and the plasma flows slowly away from other regions to enter these processes. If this be continued in one direction the whole protoplasmic mass may creep over the substratum, material being thrust out in front and drawn in from behind. It has been suggested that this form of move ment is due to variations in the surface ten sion of the protoplasmic mass. These variations may be due to unequal oxidation at different points on the surface. But nothing is known with certainty in this regard. It may be that the rotation of the protoplasm within certain walled cells is a form of amceboid movement.
Certain other forms of free movement which are sometimes confused with true locomotion are not the result of inherent energy at all, but are merely the effects of external forces. Such are the migrations of the wind-blown tumble-weeds, and of all winged seeds, pollen-grains, etc. Also the movements of certain seeds provided with hygroscopic awns are purely physical. Alternate wetting and drying cause these awns to change their form and position and thus to displace the seeds or to force them into the earth. See MOVEMENT; ROTATION.