what is tropism
Unsourced material may be challenged and removed. (September 2012). Phycomyces, a fungus, exhibiting phototropism. A tropism (from Greek ÏÏÏÏÎ¿Ï, tropos, a turning) is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus.ropisms are usually named for the stimulus involved (for example, a phototropism is a reaction to sunlight) and may be either positive (towards the stimulus) or negative (away from the stimulus).