What is Plant Tissues explain there types?

Vascular plants have separate organs to carry out specialized functions. For instance, leaves function to convert radiant energy to biochemical forms of energy; roots anchor the plant and absorb water, minerals, and nutrients; and flowers carry out reproduction. As you might imagine, these varied activities require highly specialized cells and tissues.
Single-celled organisms individually are able to perform all of the similar functions mentioned above. However, multicellular organisms clearly reflect the advantages of division of labor. Different groups of cells are assigned specific functions, and express highly specific structural and physiological characteristics that enable them to perform their assigned tasks effectively and efficiently. In other words, a cell that can concentrate most of its resources on one specific job instead of expending energy and resources obtaining food or reproduction, will be able do its job better.

The specialized cell would then be able to evolve complex structures and strategies that would help in performing its specific function. Let's take a tour of the different types of plant cells.

Dermal Cells

The protoderm produces the dermal tissues that form the outer protective covering of the plant body. This outer layer of cells is usually referred to as the epidermis. The epidermis consists of a single layer of cells, which are irregular in shape and for the most part, flattened when viewed in cross section. As the epidermal cells mature, they lay down a waxy coating of a substance called cutin, which acts like a waterproofing material. In this case, the waterproofing is designed to keep moisture and water inside the body, and thereby prevent drying out of the tissues beneath.
The general function of the epidermis is to protect the interior cells from physical damage as well as to prevent water loss. Plant cells do, however, require carbon dioxide, and they also need to rid themselves of the photosynthetic byproduct of oxygen gas. This gas exchange would not be able to occur were it not for the structures in the epidermis known as stomates, or stomata. Stomata consist of two special epidermal cells called guard cells that form pores, or openings through the epidermal layer that allow for gas exchange.

Some epidermal cells bear glands that exude toxic chemicals to prevent grazers, and others form little hair like projections, which act like spoilers to interrupt the flow of air over the surface of the leaf. In roots, the epidermal cells near the root tip create projections, or hairs through which most of the water, nutrients and minerals are absorbed.

Parenchyma Cells

Parenchyma cells are relatively undifferentiated, or unspecialized. They are what are often referred to as "typical" plant cells because they have a large central vacuole, have thin primary walls, and do not have secondary walls. There are several types of parenchyma cells that do different things in plants. Pallisade and spongy parenchyma cells with chloroplasts are found in leaves and carry out photosynthesis; storage parenchyma make up a large percentage of stems and roots; and fruits consist largely of parenchyma that store sugars.

Newly formed cells that have not yet differentiated (formed special structures) appear to be simple, basic parenchyma types of cells. They will either go on to develop the specialized characteristics, or stay the same at maturity.

Collenchyma Cells

Collenchyma cells help to support young, actively growing plants. Since young developing tissues haven't had a chance to grow thick secondary walls, collenchyma cells perform the support function with their relatively thick primary walls, and they are able to flex with the plant as it elongates. Collenchyma differs from sclerenchyma in that collenchyma cells remain alive to function, whereas sclerenchyma dies after building up lignin in their secondary cell walls. The ridges present in celery stalks that form "strings" are actually bundles of collenchyma tissue

Sclerenchyma Cells

Sclerenchyma cells function to provide support for the above ground organs of the plant. Sclerenchyma cells also have thick secondary walls that are impregnated with the hardening substance called lignin. There are two types of sclerenchyma: fibers and sclereids. Fibers are long, thin pointed cells that form bundles for strengthening the stem. Rope and hemp are made from these types of tissues.
Sclereids vary in shape and are shorter cells which are found in the outside layers of seeds and in nutshells. Sclereids provide the hardness that characterize seeds and nuts.