Wind and Other Mechanical Effects in the Development and Behavior of Plants, with Special Emphasis on the Role of Hormones

Abstract

There are three types of visible responses that are available to plants that have been mechanically stimulated: thigmonasty, thigmotropism, and thigmomorphogenesis (Fig. 1). The prefix “thigmo” indicates “touch”. A nastic response is one in which the direction of the movement is determined by anatomical constraints, and not by the direction of the stimulus. An additional characteristic of almost all nastic responses is that they are freely reversible, and may therefore be said to have the property of elasticity. The duration of the recovery period is characteristically longer than that of the motor response period. A tropic response is typically a bending movement, the direction of which is always determined by the vector of the stimulus. Tropisms often involve assymetric growth on one side of an organ, which results in its leaning toward (positive tropism) or away from (negative tropism) the stimulus vector. Tropic responses are sometimes, but not always, irreversible, and may be said to often have the property of plasticity. A morphogenetic response is one which affects the form of the plant, involves growth and/or differentiation, and is irreversible.