1. According to origin: According to origin, connective tissue is divided into three parts.
(i) Promeristem: The dividing tissue that originates from the root and apical region of the plant is called promeristem or primitive dividing tissue. It is located at the root and apex of the plant. The cells of this tissue are small, immature, vacuolated and have thin cell walls. The first growth of plants starts from this region. It is divided into different layers and forms different organs.
(ii) Primary meristem: The dividing tissue that originates in the embryonic stage of the plant is called primary meristem. It arises from early dividing tissue. This tissue is capable of dividing forever. It is located at the tip of the root, stem and branch, in the middle and at the periphery of the stem. It never becomes permanent tissue. It increases the length of the plant. Eg- fascicular cambium.
(iii) Secondary meristem: The dividing tissue that originates from the permanent tissue is called secondary meristem. This tissue is located in phellogen or cork cambium, between phases, between xylem and phloem, between two vascular bundles and in cortex. Secondary division tissue increases plant vigor. Heals plant wounds. Eg – cork cambium, interfascicular cambium etc.
2. According to cell division: According to cell division, dividing tissue is divided into three parts.
(i) Rib meristem: The dividing tissue which divides at one level is called Rib meristem. It is called rib dividing tissue because it looks like the rib of the chest. For example, spinal cord.
(ii) Plate meristem: The dividing tissue which divides into two layers is called plate meristem. Cells are single-layered and plate-like, so called squamous tissue. Division of plate dividing tissue results in flattened, elongated plant organs that increase in length and width. It increases the volume and area of plant organs. For example, the bark, leaves, etc.
(iii) Mass meristem: The dividing tissue which divides at all levels is called mass dividing tissue. It is randomly arranged to form cell islands. It increases the volume or density of plant organs. For example, embryo, follicle, endosperm, cortex, marrow etc.
3. According to location: Scientist Haberland (1914) divided dividing tissue into three parts according to location.
(i) Apical meristem: The dividing tissue located at the apex of the plant root and stem is called apical meristem. These are primary dividing tissues. It divides and causes the plant to grow in length. So the dividing tissue at the top is called growing point.
(ii) Lateral meristem: The dividing tissue which is located longitudinally along the sides of the root and stem of the plant is called lateral meristem. It causes secondary growth. It increases the height or width of the plant. Eg- Cork cambium, Interspherical cambium etc.
(iii) Intercalary meristem: The dividing tissue located between two permanent tissues is called intercalary dividing tissue. They are primary dividing tissue. It is present in the leaves, midrib, apex and flower buds of plants. Plants include rice, wheat, bamboo, grasses, horsetail (Equigitum), pine etc.
4. According to function: Scientist Haberland (1914) divided dividing tissue into three parts according to function.
(i) Protoderm: The dividing tissue that forms the skin of plants is called protoderm. Cells of this tissue form plant skin by atrial division (except bot, rubber). It forms the epiboema of the root.
(ii) Procambium: The dividing tissue that forms xylem, phloem and cambium of plants is called procambium. It is scattered in the stems of monocotyledonous plants and in ring form in the stems of dicotyledonous plants. It forms transport tissue or vascular bundles. In many plants it forms a cycle or pericycle.
(iii) Ground meristem: The dividing tissue that gives rise to cortex, pericycle, pith and medulla is called ground meristem.