In this article we will discuss about the Mechanism of Mineral Salt in Xylem.
After absorption from the soil by epiblema cells, the mineral salts pass radially inwards into the tracheary elements. With the transport of water the mineral salts also pass upwardly to reach the leaves and other parts.
That xylem is the pathway for the transport of mineral salts is based on the following facts:
1. Xylem sap contains mineral salts.
2. Salt uptake increases with the increase in the rate of transpiration and transport of water.
3. Ringing and hollowing experiments which disrupt the continuity of cortex, phloem and pith do not influence the rate of mineral uptake till the roots are metabolically active.
4. Tracer Technique. Analysis of bark and wood shows that bark (including phloem) contains more minerals than the wood although phloem is not the pathway of transport of minerals. Therefore, Stout and Hoagland (1939) inserted a paraffin paper between xylem (wood) and phloem (bark) up to a length of 23 cm (Fig. 12.9).
Radioactive potassium or phosphorous was added to the rooting medium. The concentration of radioactive mineral was found out at various levels in the stem near and in the area of separation of xylem and phloem (Table 12.5).
The data shows that in the stripped area little concentration of mineral occurs in the bark though its amount is quite high in the xylem. Greater amount of mineral in the bark above and below the strip is due to local absorption of mineral from xylem by living cells of bark but there is little translocation through it.
The pathway is only xylem. Through xylem the absorbed minerals are passed into leaves. From leaves the mineral salts reach other parts through phloem.
