Ground tissue is made up of 3 special types of cells. Parenchyma cells are the most abundant cells in plants. They form the pith in the cortex of stems, the cortex of roots, and the mesophyll of leaves. Many of these parenchyma cells are totipotent, which means they can develop into any type of cell at any time, and that's why they're involved in healing, as well as asexual reproduction. In fact, speaking of healing, sometimes you'll see what's called a callus. This is essentially a mass of unorganized parenchyma cells covering a wound. These cells rush to the scene, develop into the necessary type of cell, and help seal up the wound. Parenchyma cells also act as rays, which were mentioned previously. These radiate through the vascular tissue to transport water and nutrients laterally. Remember, it was said that xylem is responsible for vertical transport, and these cells help out by conducting lateral transport.
There are also collenchyma cells. These are primarily there for structural support and really help in the growing parts of the plant, such as growing shoots and leaves. These collenchyma cells provide structural support. They are favored in growing areas because, despite having thick cell walls and being structurally sound, they remain stretchy and flexible. This flexibility allows them to provide structural support without hindering the plant's growth by being too rigid.
Sclerenchyma cells provide structural support similar to collenchyma cells, but they are found in areas where growth has ceased. Generally speaking, sclerenchyma cells are dead at maturity. These cells have a thin primary cell wall and a very thick secondary cell wall made of lignin and cellulose. You'll find sclerenchyma cells as fibers, which have been mentioned previously. These fibers run along the xylem, for example, and help provide structural support. You'll also see sclerenchyma cells called sclereids, which have really thick lignin walls and form a protective coating on seeds and the shells of nuts, giving them a hard exterior coating on plant structures. The fibers are more involved in structural support within the tissues of plants.
Now, putting this all together, here we have all the types of cells we've talked about, the xylem, the phloem, all next to each other with their support cells, like the sclerenchyma fiber, which again is going to provide structural support. We've got a parenchyma cell that could be acting like a ray providing lateral transport of water and nutrients. We also, of course, have our collenchyma cells that are going to provide structural support in growing sections of the plant. That's all I have for this lesson. See you guys next time.