Evidences for transportation of organic materials in the phloem

Evidences for transportation of organic materials in the phloem

1. When phloem is cut, the sap exudes is rich in organic material such as carbohydrate. The fact that sap is exuded suggests that the content of the poem is under pressure.
2. The sugar content of the phloem varies with environment conditions i.e., where condition favour photosynthesis, the concentration of sugar in phloem increases indicating that phloem transport photosynthetic products.
3. Removal of a complete ring of phloem from around a stem causes an accumulation of sugars above the ring, indicating that their down progress has been interrupted.
4. If radioactive ¹⁴CO₂ is given to the plants as photosynthetic substrate, the sugar later found in phloem contain ¹⁴ when phloem and xylem are separated by waxed paper, the ¹⁴C is almost entirely found in the phloem.
5. Aphids need-like mouthparts with which they penetrate phloem in order to obtain sugars. Fluids obtained from cut mouth of anaesthetized aphid are analyzed to contain sugars.

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