4- Xylem It is the water conducting tissue which consists of vessels, tracheids, fibres and parenchyma.

1- Vessels Each vessel is formed from a series of vessel elements jointed end by end, 2ry wall is deposited in different forms: a- Annular: 2ry wall deposits as rings in narrow vessels. b- Spiral: 2ry wall forms a spiral in slightly wider vessels.

c- Reticulate: 2ry wall forms network. d- Sclariform: 2ry wall has elongated pits in vertical series. e- Pitted: 2ry wall is pitted and is formed in wider vessels. Functions: vessels are used for transport and mechanical support.

2- Tracheids Gymnosperms have tracheids only but in angiosperms the xylem consists of tracheids and vessels. The tracheids are shorter than vessels and have bordered pits on their common walls. The function of tracheids is water transport and mechanical support.

5- Phloem Phloem is the food conducting tissue which is formed of four elements; sieve elements, companion cells, parenchyma and fibres.

these include two types: a- Sieve cells: They are present in gymnosperms and lower vascular plants. They are long cells with tapering ends, having sieve areas on their walls. They have thin lining layer of cytoplasm, a large vacuole and they contain no nucleus. 1- Sieve elements

b- Sieve tubes: They are present in angiosperms. They are arranged end by end in a long series. The common walls have sieve plate with sieve area. The sieve pores are transversed by protoplasmic strands which connect the protoplast of neighboring sieve elements. Sieve tubes contain no nucleus.

these are special parenchyma cells associated with the sieve tubes of dicots and monocots. A sieve tube may has one or more companion cells. The sieve tubes and companion cells are connected by plasmodesmata. A mature companion cell has a nucleus, so there is a physiological relation between it and the sieve tube. 2- Companion cells