Shock-induced Stomatal Movements

Abstract

It is now usual in stomatal investigation to affix a porometer cup by lightly clamping the leaf between a glass plate and a glycerol-gelatin washer greased-with a beeswax-‘Vaseline’ luting-wax; this is in essence the method used by Heath¹ in his critical study of the resistance porometer. As is well known, the mechanical shock attendant on the fixing of such a cup induces almost instantaneous partial closure of the stomata in certain plants, of which Pelargonium zonale is one. The typical effect is shown in the accompanying figure: Record A, from the beginning of the record to the point II. This represents the ‘recovery curve’ of the stomata of P. zonale in continuous light after the attachment of a porometer cup, taken with a simple form of resistance porometer²; increasing manometer pressure corresponds to stomatal closure. It has for long been assumed that this smooth opening curve does, in fact, represent ‘recovery’, and that when the stomatal resistance has fallen to a conveniently low value (one to two hours being usually allowed) the stomata may be assumed to be in a substantially normal state. However, in the course of an investigation into the characteristics of shock-induced movements, an unexpected phenomenon has been encountered which throws doubt on the validity of this assumption.