Brenda has worked with K-12 students in life science, chemistry, and language arts. She holds a master's degree in Biological Sciences.
What Is Meristematic Tissue?
Think for a moment about a new, unprogrammed computer. It's a blank slate--it can potentially run any program. But once you install an operating system, all that changes. Now, the computer can only execute programs compatible with that system. Meristematic tissue is like an unprogrammed computer--it is made of cells that haven't been assigned a role within the plant, or undifferentiated cells. These cells could do or be anything, just like that blank computer. Once a cell's role is assigned though (just like when the computer is programmed), its function becomes limited.
Properties of Meristematic Cells
Cells within meristematic tissues have special characteristics that make them unique when compared to cells in mature, specialized plant tissue. Cells within meristematic tissue are self-renewing, meaning that every time they divide, one new cell remains meristematic, while the second heads off to become a programmed or specialized mature cell.
Additionally, all cells within meristematic tissue are living, while other plant tissue can be made of both living and dead cells. Meristematic cells have thin cell walls, small or no vacuoles, which are stored organelles, and large prominent nucleus. This compares to the thick walls and small nucleus of programmed cells, which also have one or more large vacuoles. Also, meristematic cells contain a significant volume of dense liquid, while specialized cells have only a small quantity of think liquid.
Types of Meristematic Tissue
Based on its location in a plant, meristematic tissues fall into two categories: primary and secondary. Both types produce new cells through mitotic division, or the splitting of the cell in two. However, the growth pattern they produce differs. Primary meristematic tissue helps the plant increase in length or vertical growth, meaning it helps the plant grow up toward the sun and down into the soil. Secondary meristematic tissue helps the plant increase the girth or lateral growth of its stems, branches, and roots. Secondary meristematic growth is also responsible for producing the bark on woody trees.
Location of Primary Meristematic Tissue
The location of primary meristematic tissue is key in understanding how it is able to produce vertical growth in the plant. In monocots, or plants with one seed leaf, primary meristematic tissue is found in the intercalary nodes. The intercalary nodes are located between areas of mature growth, kind of like the joint region on a plant. And in dicots, or plants with two seed leaves, primary meristematic tissues are found in apical regions--the tips of roots, shoots, and leaf and flower buds.
Location of Secondary Meristematic Tissue
Secondary meristematic tissues are found in all woody plants. These tissues lead to the production of cambium, which is the outer layer of wood on trees that can be visually seen when you cut a tree down and look at the cross-section.
Layering of Meristematic Tissues
In primary meristematic tissues, apical and intercalary meristems are composed of three different specialized tissue sections:
- The protoderm layer gives rise to the outermost layer of stems, roots, and leaves. This layer functions much like our own skin; it helps provide protection against physical, chemical, and elemental damage.
- The ground layer has several roles within the plant and forms the bulk of the plant. Roles include photosynthesis and gas exchange, storage and secretion of nutrients and materials, and strength and structure.
- As the name implies, the vascular layer is a transport system that provides liquid and nutrients in non-woody, herbaceous plants such as tomatoes and corn.
All secondary meristematic tissues arise from the division of cells in the cambium region, which is found in the outer layer coverings of stems and roots, or marginal areas. Cell division is very active in these areas of plants; as you move closer to the middle of the plant, cellular division is slower or has stopped completely. This leads to an outside in growth pattern found in woody plants. The cambium is divided into two main layers; each layer helps the plant in a different way and both are vital:
Vascular cambium is made up of tissues that transport nutrients and liquids, including water, from the root up to the rest of the plant.
Cork cambium consists of both living and non-living cells that replace outer layer or skin of non-woody plants. You probably already know what this is--you just call it tree bark.
Meristematic tissues enable a plant to increase in length and girth. There are two categories of meristematic tissues. Primary meristematic tissue enables vertical growth and can be found in the apical and intercalary regions of monocots and dicots. Primary meristems consist of three layers: ground layer, protoderm layer, and vascular layer.
In contrast, secondary meristematic tissues enable lateral growth and increase the girth of woody plants. Secondary meristematic tissues consist two layers: vascular cambium and cork cambium.
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