Secondary growth - Wikipedia
Shmoop Biology explains Primary Growth and Secondary Growth. In between the leaf primordia, where new leaves form, and the stem below, are the axillary buds. Storing nutrients; Associating with soil microbes in symbiotic relationships. In this activity we will explore the relationship between primary and secondary growth in plants. Plant stems and roots grow in length by primary growth and in. Differentiate between primary and secondary growth; Identify and describe the roles of apical vs lateral meristems in plant growth; Compare.
As it grows it develops xylem and phloem, which become connected with the vascular tissues of the main root. This process is very different from that which takes place in shoots, where lateral branches forming stems or leaves originate only from the apical meristematic tissue of the shoot.
Lateral roots can develop large distances away from the root tip. Subsequent cell elongation then leads to primary growth. In many plants, most primary growth occurs primarily at the apical top bud, rather than axillary buds buds at locations of side branching.
What is the difference between primary growth and secondary growth?
The influence of the apical bud on overall plant growth is known as apical dominance, which prevents the growth of axillary buds that form along the sides of branches and stems. Most coniferous trees exhibit strong apical dominance, thus producing the typical conical Christmas tree shape. If the apical bud is removed, then the axillary buds will start forming lateral branches.
Gardeners make use of this fact when they prune plants by cutting off the tops of branches, thus encouraging the axillary buds to grow out, giving the plant a bushy shape. Secondary growth in shoots and roots The process of secondary growth is controlled by the lateral meristems, and is similar in both stems and roots.
Lateral meristems include the vascular cambium and, in woody plants, the cork cambium cambium is another term for meristem. Herbaceous non-woody plants mostly undergo primary growth, with hardly any secondary growth or increase in thickness. Secondary growth, or wood, is noticeable in woody plants; it occurs in some dicots, but occurs very rarely in monocots.
- Plant Development II: Primary and Secondary Growth
- Difference Between Primary and Secondary Growth in Plants
The details below are specific to secondary growth in stems. While the principles are similar for secondary growth in roots, the details are somewhat different. We will discuss only the details specific to stems. The vascular cambium is located between the primary xylem and primary phloem within the vascular bundle.
Recall that xylem is located toward the interior and phloem toward the exterior of the bundle. The cells of the vascular cambium divide and form secondary xylem tracheids and vessel elements to the inside, and secondary phloem sieve elements and companion cells to the outside.
The cells of the secondary xylem contain lignin, the primary component of wood, which provides hardiness and strength. In woody plants, cork cambium is the outermost lateral meristem. It produces cork cells, which contain a waxy substance that can repel water. The phloem together with the cork cells form the bark, which protects the plant against physical damage and helps reduce water loss.
The cork cambium also produces a layer of cells known as phelloderm, which grows inward from the cambium. The cork cambium, cork cells, and phelloderm are collectively termed the periderm. The periderm substitutes for the epidermis in mature plants.
The combined actions of the vascular and cork cambia together result in secondary growth, or widening of the plant stem. These structures are illustrated below: In woody plants, primary growth is followed by secondary growth, which allows the plant stem to increase in thickness or girth. Secondary vascular tissue is added as the plant grows, as well as a cork layer.
The bark of a tree extends from the vascular cambium to the epidermis. OpenStax Biology A new layer of xylem and phloem are added each year during the growing season. The interior xylem layers eventually die and fill with resin, functioning only in structural support.
The interior, nonfunctional xylem is called heartwood. The exterior layers of phloem eventually become crushed against the cork cambium and are broken down.
Thus a mature tree contains many interior layers of older, nonfunctional xylem deep within the stem, but only a small amount of older phloem. The layers of tissues within a mature tree trunk. Image based on work by Brer Lappin — Public Domain, https: Secondary Growth and Annual Rings The activity of the vascular cambium results in annual growth rings.
During the spring growing season, cells of the secondary xylem have a large internal diameter and their primary cell walls are not extensively thickened. This is known as early wood, or spring wood.
The lateral meristem is composed of the vascular cambium and the cork cambium. The vascular cambium is located in between the primary xylem and primary phloem. The cells of the vascular cambium that are next to the primary phloem divide to form the secondary phloem.
The secondary phloem consists of sieve elements and companion cells. The cells near to the primary xylem forms the secondary xylem, which consists of tracheids and vessels. The activity of the vascular cambium during the summer and the winter give rise to annual growth rings. The cells in the bark contain a waxy substance called suberin, which reduces the water loss.
The phelloderm layer of the bark grows towards the stele. The phelloderm, cork cambium, and the cork cells are collectively called the periderm. In mature plants, the epidermis is replaced by the periderm. The lenticels are the openings of a mature stem through which the gas exchange occurs. A mature Pinus stem is shown in figure 2. Similarities Between Primary and Secondary Growth Primary and secondary growth are involved in increasing the size of the plant. Both primary growth and secondary growth occur in woody plants.
What is the difference between primary growth and secondary growth?
The meristematic tissue is involved in both primary and secondary growth of the plant. Primary growth is the growth that occurs by the action of the primary meristem, which increases the length of the stem and adds appendages to the stem.
Secondary growth is the growth that occurs by the action of the cambium, which increases the diameter of the plant. Occur by Primary Growth: The primary growth occurs by the action of the apical meristem. The secondary growth occurs by the action of the lateral meristem. The primary growth results in the growth in the longitudinal axis. The secondary growth results in the radial growth.
The primary growth of the plant occurs at the beginning. The secondary growth follows the primary growth.