What is correct for $P$ in the given diagram representing the pressure flow hypothesis?

Mass flow hypothesis was first described by

If a stem is girdled,what happens?

Arrange the following events of mass flow of organic material in sequence:
$I$. Sugars are transported from cell to cell in the leaf
$II$. Food is synthesized in form of glucose by leaf cells
$III$. Movement of water takes place into sieve tube elements
$IV$. Downward movement of sugar occurs in the stem
$V$. Solutes are actively transported into the sieve elements

Which theory best explains the translocation of organic solutes?

Marshall and Wardlaw proposed the theory of