In a girdled plant, when water is supplied to the leaves above the girdle, leaves may remain green for sometime because leaves can synthesise their own carbohydrate food through photosynthesis, then wilt due to non-availability of water. The system of xylem vessels from root to the leaf vein can supply the needed water, during girdling there is a possible loss of xylem vessels and the water supply cuts off, resulting in death of plant.

Various types of ions, minerals and organic compound are transported in plants in various modes, e.g.,

(i) Food substances synthesised in leaves are translocated downward towards root and stem.

(ii) Similarly food is translocated upwards to the developing leaves, buds and fruits.

(iii) Radial transport of food occurs across the stem from the cells of pith, from cortex etc, towards epidermis.

(iv) lons and minerals are transported upwards through xylem.

Since, diffusion is a slow process and allows movement of molecules for short distances only, it cannot filled and alone carry out the above mentioned movements of organic and inorganic substances. Therefore, a need arises for special long distance transport systems that permits and move substances at a much faster rate, i.e., mass or bulk flow system through conducting tissues (translocation).

Under conditions of limited water supply, plants reduce the loss of water through transpiration by shutting down stomata. But they carry out the important life processes like photosynthesis, respiration and transport of food, etc.

No, the ascent of sap is not possible without the cohesive and adhesive properties of water as they play an important role in transport of water because of the following reasons

(i) Cohesion forces hold together the water molecule in the conducting channels, so vacuum is not created.

(ii) Adhesive forces between the water molecule and cellulose of cell wall make a thin film of water along the channels so, this film can be pulled up by transpiration pull drawing more and more water upwards in the conducting channels from the root.

Yes, it shows that xylem tissue conducts water.