What is the Difference Between Endarch and Exarch

The main difference between endarch and exarch is that the endarch is the occurrence of protoxylem towards the center and metaxylem towards the periphery in the stem of the seed plants whereas exarch is the occurrence of protoxylem towards the periphery and metaxylem towards the center in the root of vascular plants. 

Endarch and exarch are two types of primary xylem development in vascular land plants. Endarch arrangement results in the centrifugal pattern of development while the exarch arrangement results in the centripetal pattern of development.

Key Areas Covered

1. What is Endarch
     – Definition, Arrangement, Importance
2. What is Exarch
     – Definition, Arrangement, Importance
3. What are the Similarities Between Endarch and Exarch
     – Outline of Common Features
4. What is the Difference Between Endarch and Exarch
     – Comparison of Key Differences

Key Terms

Endarch, Exarch, Metaxylem, Primary Xylem development, Protoxylem

What is Endarch

Endarch is one of the primary xylem arrangement in which the protoxylem occurs towards the center of the pith while the metaxylem occurs in the periphery. Here, protoxylem and metaxylem are the two types of xylem tissue involved in distinguishing between different types of primary xylem development. Generally, protoxylem matures first and metaxylem develops later. The cells of the protoxylem are smaller than the cells in the metaxylem. Since protoxylem matures first, endarch refers to the development from the center. Therefore, protoxylem occurs at the center while the metaxylem, which matures later, occurs in the periphery.

Figure 1: Arrangement of Protoxylem and Metaxylem in the Dicot Stem

Significantly, the endarch development of the primary xylem tissue occurs in the stem of the seed plants. This type of development is identified as a centrifugal development.

What is Exarch

Exarch is another type of primary xylem development in which the protoxylem occurs towards the periphery while the metaxylem occurs towards the center. Here, the protoxylem, which matures first, occurs at the periphery and the metaxylem, which matures later, occurs in the center. Therefore, exarch refers to the development from the periphery. Hence, the youngest cells of the xylem occur at the center.

Figure 2: Primary Xylem Development

Moreover, exarch development can be identified in the root of vascular plants. It gives rise to a centripetal development.

Similarities Between Endarch and Exarch

• Endarch and exarch are two of the four types of primary xylem development patterns. The other two are centrarch and mesarch.
• They are classified based on the arrangement of protoxylem and metaxylem in the primary xylem tissue.
• Also, more than one strands of primary xylem develop in both endarch and exarch.
• Besides, these arrangements can occur in both stem and root.

Difference Between Endarch and Exarch           

Definition

Endarch refers to the development from the center; having the oldest cells closest to the core in the xylem while exarch refers to the development from the periphery; having the youngest cells closest to the core in the xylem. Thus, this is the fundamental difference between endarch and exarch.

Protoxylem

Moreover, the direction of protoxylem is a major difference between endarch and exarch. Protoxylem occurs towards the center in the endarch arrangement while protoxylem occurs towards the periphery in the exarch arrangement.

Metaxylem

Metaxylem occurs towards the center in the endarch arrangement while metaxylem occurs towards the periphery in the exarch arrangement. Hence, this is also a major difference between endarch and exarch.

Occurrence

Furthermore, endarch xylem arrangement occurs in the stem of the seed plants while the exarch arrangement occurs in the root of vascular plants.

Result in

Besides, endarch arrangement results in the centrifugal pattern of development while exarch arrangement results in the centripetal arrangement. This is another difference between endarch and exarch.

Conclusion

Endarch is a type of primary xylem arrangement in which the protoxylem occurs towards the center of the pith while metaxylem occurs towards the periphery. This type of xylem arrangement occurs in the stem of flowering plants. In comparison, exarch is another type of primary xylem development, which occurs in the root. Here, protoxylem occurs towards the periphery while metaxylem occurs towards the center. Therefore, the main difference between endarch and exarch is the direction of the protoxylem and metaxylem.

References:

1. Gilmore, Michael. “Xylem Development.” Study Notes: Trickster, Available Here.

Image Courtesy:

1. “Woody Dicot Stem: Proto and Metaxylem in One Year Liriodendron” Berkshire Community College Bioscience Image Library (Public domain) via Flickr
2. “Xylem Development” By Peter coxhead – Own work (CC0) via Commons Wikimedia