Marshall and Wardlaw proposed the theory of

During translocation,the carbohydrates are relatively richer in:

According to the pressure flow hypothesis:
$A.$ Phloem loading produces a hypertonic condition in the sieve tubes.
$B.$ Water potential gradient facilitates the mass movement in the phloem.
$C.$ Phloem unloading is a passive process.

Aphid stylet sap analysis can be used to know

Analogy type questions:
$(1)$ In Xylem : Vessel :: In Phloem : ..........
$(2)$ Synthesis of food : Source :: Regions of need : ...........

Based on various pieces of evidence,it is known that the downward movement of food in plants takes place through: