What makes plants capable of determinate growth

Apical meristems contain meristematic tissue located at the tips of stems and roots, which enable a plant to extend in length. Lateral meristems facilitate growth in thickness or girth in a maturing plant. Intercalary also called basal meristems occur only in some monocots, at the bases of leaf blades and at nodes the areas where leaves attach to a stem.

This tissue enables the monocot leaf blade to increase in length from the leaf base; for example, it allows lawn grass leaves to elongate even after repeated grazing or mowing.

Primary growth is controlled by root apical meristems or shoot apical meristems , while secondary growth is controlled by the two lateral meristems, called the vascular cambium and the cork cambium.

Not all plants exhibit secondary growth. The video below provides a nice discussion of primary and secondary growth in plants beginning at :. Root growth begins with seed germination. When the plant embryo emerges from the seed, the radicle of the embryo forms the root system.

The tip of the root is protected by the root cap , a structure exclusive to roots and unlike any other plant structure. The root cap is continuously replaced because it gets damaged easily as the root pushes through soil. Behind the root cap, within the first centimeter or so, the root tip can be divided into three zones:. The root tip is divided into three areas: an upper area of maturation, a middle area of elongation, and a lower area of cell division at the root tip.

In the area of maturation, root hairs extend from the main root and cells are large and rectangular. The area of elongation has no root hairs, and the cells are still rectangular, but somewhat smaller.

A vascular cylinder runs through the center of the root in the area of maturation and the area of elongation. In the area of cell division the cells are much smaller. Cells within this area are called the apical meristem.

A layer of cells called the root cap surrounds the apical meristem. Image credit: OpenStax Biology. Plants may also have lateral roots that branch from the main tap root.

The lateral roots originate from meristematic tissue in the pericycle , which is the outermost cell layer in the vascular cylinder in the center of the root shown below. Once they have emerged, lateral roots then display their own primary growth, continually adding length to the lateral root. Staining reveals different cell types in this light micrograph of a wheat Triticum root cross section.

Sclerenchyma cells of the exodermis and xylem cells stain red, and phloem cells stain blue. Other cell types stain black. The stele, or vascular tissue, is the area inside endodermis indicated by a green ring. Root hairs are visible outside the epidermis. The image is of a transverse section of part of a root of the monocot Maize Zea mays showing the stele and a lateral root.

Lateral roots develop from a layer of cells underneath the endodermis, called the pericycle. They originate by cell division of pericycle cells opposite a protoxylem group. The root starts to swell as the new lateral root penetrates outwards towards the surface, pushing its way through cortical parenchyma cells and finally bursting out through the epidermis into the soil.

Meristematic tissues are found in many locations, including near the tips of roots and stems apical meristems , in the buds and nodes of stems, in the cambium between the xylem and phloem in dicotyledonous trees and shrubs, under the epidermis of dicotyledonous trees and shrubs cork cambium , and in the pericycle of roots, producing branch roots.

The two types of meristems are primary meristems and secondary meristems. Its main function is to trigger the growth of new cells in young seedlings at the tips of roots and shoots and forming buds. Apical meristems are organized into four zones: 1 the central zone, 2 the peripheral zone, 3 the medullary meristem and 3 the medullary tissue.

Meristematic zones : Each zone of the apical meristem has a particular function. Pictured here are the 1 central zone, 2 peripheral zone, 3 medullary meristem and 3 medullary tissue. Its main function is to begin growth of new cells in young seedlings at the tips of roots and shoots forming buds, among other things. The central zone is located at the meristem summit, where a small group of slowly dividing cells can be found.

Cells of this zone have a stem cell function and are essential for meristem maintenance. The proliferation and growth rates at the meristem summit usually differ considerably from those at the periphery.

Surrounding the central zone is the peripheral zone. The rate of cell division in the peripheral zone is higher than that of the central zone. Peripheral zone cells give rise to cells which contribute to the organs of the plant, including leaves, inflorescence meristems, and floral meristems.

An active apical meristem lays down a growing root or shoot behind itself, pushing itself forward. They are very small compared to the cylinder-shaped lateral meristems, and are composed of several layers, which varies according to plant type.

The outermost layer is called the tunica, while the innermost layers are cumulatively called the corpus. A variety of genes control flower development, which involves sexual maturation and growth of reproductive organs as shown by the ABC model. Flower development is the process by which angiosperms produce a pattern of gene expression in meristems that leads to the appearance of a flower. A flower also referred to as a bloom or blossom is the reproductive structure found in flowering plants.

There are three physiological developments that must occur in order for reproduction to take place:. Anatomy of a flower : Mature flowers aid in reproduction for the plant.

In order to achieve reproduction, the plant must become sexually mature, the apical meristem must become a floral meristem, and the flower must develop its individual reproductive organs. A flower develops on a modified shoot or axis from a determinate apical meristem determinate meaning the axis grows to a set size. The transition to flowering is one of the major phase changes that a plant makes during its life cycle. 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.

The increase in stem thickness that results from secondary growth is due to the activity of the lateral meristems, which are lacking in herbaceous plants. Lateral meristems include the vascular cambium and, in woody plants, the cork cambium. The vascular cambium is located just outside the primary xylem and to the interior of the primary phloem.

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 thickening of the stem that occurs in secondary growth is due to the formation of secondary phloem and secondary xylem by the vascular cambium, plus the action of cork cambium, which forms the tough outermost layer of the stem. The cells of the secondary xylem contain lignin, which provides hardiness and strength. In woody plants, cork cambium is the outermost lateral meristem. It produces cork cells bark containing a waxy substance known as suberin that can repel water.

The bark 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. In some plants, the periderm has many openings, known as lenticels, which allow the interior cells to exchange gases with the outside atmosphere.

This supplies oxygen to the living- and metabolically-active cells of the cortex, xylem, and phloem. The activity of the vascular cambium gives rise to annual growth rings. During the spring growing season, cells of the secondary xylem have a large internal diameter; their primary cell walls are not extensively thickened.