Simple permanent tissue walls of whose cells are unevenly thickened by additional cellulose deposition are called collenchyma. Collenchyma cells have no intercellular spaces between them. They have a distinct nucleus and dense cytoplasm.

Xylem and Phloem are the two types of complex tissues, also called conducting tissues or vascular tissues, and together they form vascular bundles. The complex permanent tissue associated with the conduction of water and mineral salts in vascular plants is called the xylem. Xylem is a complex tissue as it consists of different types of cells, both living and non-living, namely-Tracheid, Trachea or Xylem vessels, Xylem parenchyma or Wood parenchyma and Xylem fibre or Wood fibre.

Xylem and Phloem are the two types of complex tissues, also called conducting tissues or vascular tissues, and together they form vascular bundles. Complex permanent vascular tissue responsible for transporting food in the plant body is called phloem. The components of phloem are sieve tubes, companion cells, phloem fibres or bast fibres and phloem parenchyma.

Spherical or isodiametric, or oval cells with unevenly very much thickened walls are called sclereids or stone cells. They are shorter in size with many pits on their walls. Walls of sclereids are hard and lignified, also called stone cells or grit cells. They give hardness to the seed coat. We get a crunchy and granular feeling when we chew pear fruit because of the presence of sclereids.