Chapter : 3. Transportation
Some materials (gases) pass in and out of plants through diffusion. Other materials required for building plant body are obtained from soil, e.g. , nitrogen, phosphorus, other minerals, water. They have to be transported to long distances depending upon the size of the plant. There are two independent pathways having conducting tubes. One is xylem that moves water and minerals from soil to aerial parts. The other is phloem which carries food from the region of availability (e.g, leaves, storage organs) to the areas of utilsation.
Xylem (Wood) : It is a complex tissue which transports sap (water and minerals). Xylem has four types of cells–xylem fibres, xylem parenchyma, tracheids and vessels. Vessels and tracheids are called tracheary elements because they take part in transport of sap. Both the tracheary elements have lignified wall .
Phloem : It is complex tissue which takes apart in transport of food. Phloem has four types of cells – sieve tubes, companion cells, phloem parenchyma and phloem fibres. Only phloem fibres are dead cells. Other are living cells.
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