What is the Difference Between Eustele and Atactostele

The main difference between eustele and atactostele is that eustele contains vascular bundles in one or two rings. But, atactostele contains numerous vascular bundles, scattered throughout the stem. Furthermore, eustele occurs in the stem of dicots and the root of monocots, but atactostele occurs in the stem of monocots.  

Eustele and atactostele are two types of siphonostele, occurring in the stem and the root of seed plants. Generally, siphonostele is a type of arrangement of the stele always with a ground tissue known as the pith internal to the xylem. 

Key Areas Covered 

1. What is Eustele
     – Definition, Structure, Occurrence
2. What is Atactostele
     – Definition, Structure, Occurrence
3. What are the Similarities Between Eustele and Atactostele
     – Outline of Common Features
4. What is the Difference Between Eustele and Atactostele
     – Comparison of Key Differences

Key Terms 

Atactostele, Dicot Stem, Eustele, Monocot Stem, Stele

What is Eustele 

Eustele is the type of arrangement of the vascular bundle in the dicot stem. The main characteristic feature of it is the presence of a recognizable one or two rings of vascular bundles. Furthermore, these vascular bundles are collateral, containing the xylem on one side and the phloem on the other side. In addition to that, a central pith is present in the eustele made up of ground tissue. However, it lacks an endodermis, surrounding the vascular bundle. Only the parenchymal cells surround the vascular bundles.

Figure 1: Dicot Stem

In general, eustele is one of the several types of vascular bundle arrangement, which belong to the siphonostele. Usually, the main characteristic feature of the siphonostele is the presence of a central pith surrounded by the vascular tissue. Apart from the dicot stem, eustele also occurs in the root of monocots. 

What is Atactostele 

Atactostele is a variation of the eustele, being more complex. That means, it contains numerous vascular bundles, scattering throughout the stem. Also, it does not contain a central pith.

Figure 2: Monocot Stem

Basically, this type of vascular bundle arrangement occurs in the stem of monocots including corn, Zea mays, etc. 

Similarities Between Eustele and Atactostele  

• Eustele and atactostele are two types of vascular tissue arrangements.  
• Generally, both are types of siphonostele in which a ground tissue called the pith internal to the xylem.  
• Also, they occur in seed plants. 
• They contain both protoxylem and metaxylem.  
• Their function is to conduct water and sugar accordingly through the stem. 

Difference Between Eustele and Atactostele

Definition 

Eustele refers to a type of siphonostele, in which the vascular tissue in the stem forms a central ring of bundles around a pith. But, atactostele refers to a type of eustele, found in monocots, in which the vascular tissue in the stem exists as scattered bundles.  

Occurrence 

Eustele occurs in the stem of dicots and the root of monocots, while atactostele occurs in the stem of monocots.  

Vascular Bundles 

Vascular bundles arranged in the form of rings in the eustele, but vascular bundles are scattered in the atactostele. 

Number of Vascular Bundles 

Around 4 to 8 vascular bundles occur in eustele, while numerous vascular bundles occur in atactostele. 

Size of Vascular Bundles 

All vascular bundles are equal in size in eustele, but the outer vascular bundles are smaller than the inner vascular bundles in atactostele. 

Sclerenchymatous Bundle Cap 

Vascular bundles in eustele do not contain a sclerenchymatous bundle cap, while the vascular bundles in the atactostele contain a sclerenchymatous bundle cap.  

Sclerenchymatous Bundle Sheath 

Vascular bundles in eustele are not surrounded by a bundle sheath, while the vascular bundles of atactostele are surrounded by a sclerenchymatous bundle sheath. 

Metaxylem 

Many metaxylem elements are present in eustele, but only two metaxylem elements are present per vascular bundle in atactostele. 

Protoxylem Lacuna 

Protoxylem lacuna is absent in the eustele, while protoxylem lacuna is present in the atactostele. 

Xylem Elements 

The xylem elements of the eustele are polygonal while the xylem elements of the atactostele are circular. 

Phloem Parenchyma and Phloem Fibers 

Both phloem parenchyma and phloem fibers occur in the eustele, but both phloem parenchyma and phloem fibers are absent in the atactostele. 

Pith 

Eustele contains a pith, while atactostele does not contain a pith.  

Medullary Rays 

Medullary rays occur in the eustele, while medullary rays occur in the atactostele.  

Pericycle 

The pericycle is present in the eustele, but the pericycle is absent in the atactostele. 

Differentiation of Ground Tissue 

The ground tissue of eustele is differentiated into steler and extra-steler tissue, while the ground tissue of the atactostele is not differentiated into steler and extra-steler tissue.  

Conclusion 

In brief, eustele is a type of siphonostele, containing vascular bundles arranged in one or two rings. Generally, 4 to 8 of such vascular bundles occur in the stem of dicots. Also, a central pith occurs internally to the xylem. Additionally, eustele also occurs in the root of the monocots. On the other hand, atactostele is a variation of eustele, containing numerous vascular bundles, which occur scattered throughout the stem. Usually, atactostele occurs in the monocot stem. In conclusion, the main difference between eustele and atactostele is the arrangement of vascular bundles and occurrence. 

References:

1. “Roots, Stems, and Steles.” Psilotum, Available Here.

Image Courtesy:

1. “Botana curus monocot stem 40×” By Kelvinsong – Own work (CC BY 3.0) via Commons Wikimedia   
2. “Herbaceous Dicot Stem: Vascular Bundles in Younger Trifolium” By Berkshire Community College Bioscience Image Library (Public domain) via Flickr