What is the Difference Between Stele and Vascular Bundle

The main difference between the stele and vascular bundle is that stele is the central part of the stem and root whereas the vascular bundle is a part of the stele containing the xylem and phloem, and cambium.

The stele and vascular bundle are two parts of the central stem and root. Generally, the stele includes the primary vascular tissue, medullary rays, the pericycle, and the pith.

Key Areas Covered

1. What is Stele
   • Definition, Features, Importance
2. What is Vascular Bundle
   • Definition, Features, Importance
3. Similarities Between Stele and Vascular Bundle
   • Outline of Common Features
4. Difference Between Stele and Vascular Bundle
   • Comparison of Key Differences

Key Terms

Stele, Vascular Bundle, Xylem

What is Stele

Generally, the stele is the central part of the stem. It stele contains the cells from procambium. The three components of the stele are the vascular tissue, pith, and pericycle. The epidermis, which is the innermost cell layer of the cortex, occurs outside of the stele. There are two types of stele: they are protostele and siphonostele. The early vascular plants contain the protostele. It also contains a central core of vascular tissue. In general, it contains the cylindrical strand of the xylem, surrounded by a region of phloem. However, the endodermis occurs surrounding the protostele. In addition, there are three types of protostele: haplostele, actinostele, and plectostele.

Figure 1: Protostele Types

Among them, haplostele contains a cylindrical core of the xylem surrounded by a ring of phloem. Whereas, the actinostele is a variation of the protostele in which the core is lobed or fluted. Meanwhile, plectostele contains plate-like regions of the xylem. Furthermore, the second type of stele, the siphonostele, contains the central region of ground tissue called the pith. Moreover, there are three types of siphonostele: the solenostele, dictyostele, and eustele.

Figure 2: Siphomostele Types

Among them, the solenostele arrangement occurs in ferns and it contains a single leaf gap. Whereas, dictyostele arrangement occurs only in ferns. It usually contains multiple leaf gaps. While, the third arrangement, eustele is ectophloic, which means that phloem occurs only in the external section of the xylem.

What is Vascular Bundle

The vascular bundle is the transport system of the plant. The two types of transport systems of plants are the xylem and the phloem. Other than them, the vascular bundle contains supportive and protective tissues. In between the xylem and phloem, there is cambium tissue. In both stem and root, the xylem typically lies towards the axis (adaxial) with the phloem positioned away from the axis (abaxial). Meanwhile, in the leaf, the adaxial surface of the leaf will usually be the upper side, with the abaxial surface the lower side.

Figure 3: Vascular Bundle Types

Moreover, the basic types of cells of a vascular bundle include parenchyma, sclerenchyma, and collenchyma cells. In addition to that, there are various types of vascular bundles: (A) concentric, periphloematic, (B) concentric, perixylematic, (C) radial with inner xylem, here with four xylem-poles, left closed, right open, (D)  collateral closed, (E) collateral open, (F) bicollateral open, as described in figure 3.

Concerning the functions, the main function of the vascular bundle is to transport water and food throughout the plant while providing structural support to the plant.

Similarities Between Stele and Vascular Bundle

• The stele and the vascular bundle are the central part of the stem and root.
• Moreover, their function is to transport water and nutrients throughout the plant and to provide structural support to the plant.

Difference Between Stele and Vascular Bundle

Definition

Stele refers to the central core of the stem and root of a vascular plant, consisting of the vascular tissue (xylem and phloem) and associated supporting tissue, while vascular bundle refers to a strand of conducting vessels in the stem or leaves of a plant, typically with phloem on the outside and xylem on the inside.   

Components

Usually, parts of the stele include vascular tissue, pith, and pericycle, while parts of a vascular bundle include the xylem, phloem, and cambium.

Importance

The stele provides structural support to the plant while the vascular bundle transports water and nutrients throughout the plant.

Conclusion

In brief, the stele is the central part of the vascular plant’ stem and root. It also contains the pith, pericycle, and vascular tissue. The main function of the stele is to provide structural support to the plant. On the other hand, there are several types of vascular tissue arrangements in the stele depending on the occurrence of the xylem and phloem tissue. The main function of the vascular bundle is to transport water and nutrients throughout the plant. Also, there are several vascular tissue arrangements in the vascular bundle. However, the main difference between stele and vascular bundle is their arrangements and function.

References:

1. Wikimedia Foundation. (2022, March 22). Stele (biology). Wikipedia. Retrieved August 24, 2022.
2. Wikimedia Foundation. (2022, March 20). Vascular bundle. Wikipedia. Retrieved August 24, 2022.

Image Courtesy:

1. “Protostele ” By EncycloPetey – Own Work (Public Domain) via Commons Wikimedia
2. “Siphonostele ” By EncycloPetey – Own Work (Public Domain) via Commons Wikimedia
3. “Leitbündel” By RobKohl – Own Work (CC BY-SA 3.0) via Commons Wikimedia