Lewitt's explanation for stomatal action is due to

When is the transpiration pull generated?

Phenylmercuric acetate $(PMA)$ results in which of the following effects?

The factor, most important in regulating transpiration, is

The trunk of a tree shrinks in the day due to

Read the following statements carefully and choose the right answer from the codes given below:
$I$. $PMA$ and silicon oil of low viscosity are considered as antitranspirants.
$II$. $BAP$,$NAA$,and cobalt chloride are also used as antitranspirants.
$III$. Abscisic acid $(ABA)$ affects the mechanism of opening and closing of stomata.
$IV$. Starch of guard cells is converted into $PEP$ (phosphoenolpyruvate) ions by the process of hydrolysis.
$V$. Potometer works on the principle of potential difference between the tip of the tube and that of the plant.
$VI$. Transpiration rate is directly proportional to the relative humidity.