In tall trees the distance to which water is transported may be more than 30 metres. A very strong force must be built up in the plant for pushing water to such great heights. This force has two components:
1. As water diffuses from one cell to the next, an unbroken column of water is formed. Continuous diffusion of water from the root cells pushes the water upward.
2. Water is constantly lost through the leaf surface due to transpiration. This creates a pull and the water column is pulled from above.
Thus, due to the combined effect of the pulling pushing forces, water reaches different parts of the plant body.
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Transport of food material from the leaves to the needy and storage organs of plant is called translocation. Phloem carries the food from leaves to different parts of the plant. Translocation of food takes place by the process of simple diffusion.