The only gaseous plant hormone is . . . . . . .

Write an explanatory note on Ethylene.

$I.$ More female flowers in cucumber
$II.$ $\alpha$-amylase production in barley grain
$III.$ Acceleration of fruit ripening in tomato
$IV.$ Delay in sprouting in potato tubers
From the given effects,identify the effects of ethylene and choose the correct option accordingly.

Which plant growth regulator can be classified as both a growth inhibitor and a growth promoter?

'Climacteric' is

$PGR$ which was discovered by Cousins .........