Experiments to demonstrate bidirectional movement in a single sieve tube are technically very difficult to perform.
2.
Some experiments indicate that bidirectional movement may occur in a single sieve tube, whereas others do not.
3.
If the mechanism of translocation operates according to pressure flow hypothesis, bidirectional movement in a single sieve tube is not possible.
4.
An objection leveled against the pressure flow mechanism is that it does not explain the phenomenon of bidirectional movement i . e . movement of different substances in opponent directions at the same time.
5.
The phenomenon of bidirectional movement can be demonstrated by applying two different substances at the same time to the phloem of a stem at two different points, and following their longitudinal movement along the stem.
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