The New Student's Reference Work/Chemotaxis

Chem′otax′is (in plants), the sensitiveness of an organism, free to move about, to a one-sided chemical stimulus (see Irritability), to which it responds by taking up a definite attitude with respect to the direction from which the substance is diffusing. Since no plants (except possibly the myxomycetes or slime-moulds, which see) are free to orient themselves thus unless they are immersed in water, it follows that the substance in order to act must be soluble and diffusible in water. Thus the sperms (male cells) of mosses will so place themselves in a diffusing current of sugar particles that, as they swim, they move toward the source of the sugar. Such agencies are believed to determine the movement of the sperms toward the egg in many plants.