Difference Between Apical and Lateral Meristems

Main Difference – Apical Meristem vs Lateral Meristem

In plants, meristematic tissue consists of young living cells that are capable of continuously dividing and are responsible for the plant growth. Apical meristem, lateral meristem, and intercalary meristem are the three types of meristematic tissues which differ in their position. The apical meristem is present in the apex of stem and roots. The lateral meristem is present in the sides of stem and roots and the intercalary meristem is present between the tip and the base of the stem and leaves. The intercalary meristem is involved in the increase of length between nodes. The main difference between apical meristem and lateral meristem is that apical meristem is involved in the primary growth of the plant that increases the length at the apex whereas lateral meristem is involved in the secondary growth of the plant that increases in diameter. 

1. What is Apical Meristem
     
– Definition, Characteristics, Function
2. What is Lateral Meristem
     
– Definition, Characteristics, Function
3. What is the difference between Apical and Lateral Meristems
Difference Between Apical and Lateral Meristems - Comparison Summary

What is Apical Meristem

The apical meristem is the meristematic tissue found at the apex of stem and roots. It is involved in the primary growth of the plant by increasing the length of the plant. In the root, the meristem is situated behind the tip (sub-terminal) and in the shoot, it is the terminal. Cells in the apical meristem are unspecialized and actively divide to produce new cells throughout the lifetime of a plant. Once divided, the cells in the apex remain undifferentiated and undergo continuous cell division by mitosis. But cells in the center of the plant gradually lose their power of division and become a permanent tissue. The central cells are vacuolated and expanded by absorbing water by the vacuole. Then, they are specialized to perform a particular function.

While becoming a permanent tissue, the central cells in the apical meristem are first differentiated into protoderm, procambium and ground meristem. The protoderm is differentiated into the epidermis. The plant’s vascular tissue, xylem, and phloem are differentiated from procambium. Ground meristem is differentiated into the ground tissue that houses chloroplasts for photosynthesis, stores food in the form of starch, and provides support to the plant. A photomicrograph of a Coleus stem tip is shown in figure 1.

Main Difference - Apical vs Lateral Meristem

Figure 1:  Coleus stem tip
A – Procambium, B- Ground meristem, C – leaf gap, D – Trichome, E – Apical meristem, F – Developing leaf primordia, G – Leaf primordium, H – Axillary bud, I – Developing vascular tissue

What is Lateral Meristem

The lateral meristem lies laterally in the stem and roots and is involved the secondary growth. Secondary growth only occurs in dicots. The lateral meristem is responsible for the thickening of the vascular cambium and the cork cambium. Vascular cambium produces both secondary xylem and secondary phloem. The secondary xylem is produced inside the stem and the secondary phloem is produced in the stem periphery. The stem tissue that is produced by the secondary xylem is called wood. Secondary phloem produces the inner bark. Due to the favorable conditions that are provided during the summer such as intense sunlight, vascular cambium actively divides. But in the winter, the division of the vascular cambium occurs slowly due to the reduced intense of sunlight. This differential growth of the vascular cambium produces annual rings in the stem. The number of rings in the stem hence determines the age of the tree.

Cork cambium, which lies closer to the surface, produces the outer bark (periderm). The outer bark is made up of dead cells, replacing the epidermis in woody stems.  The cells in the vascular cambium are thin-walled and highly vacuolated. The cork cambium is originated during the differentiation of permanent tissue. It serves as the secondary lateral meristem. The secondary components of the stem are shown in figure 2.

Difference between Apical and Lateral Meristem

Figure 2: Secondary components of the stem

Difference Between Apical and Lateral Meristem

Definition

Apical Meristem: Apical meristem is the meristematic tissue in the apex of stem and roots, which is responsible for the primary growth of the plant.

Lateral Meristem: Lateral meristem is the meristematic tissue in the sides of stems and roots, which is responsible for the secondary growth of the plant.

Growth 

Apical Meristem: The apical meristem increases the length of the plant at the apex of stem and roots.

Lateral Meristem: The lateral meristem increases the diameter of stem and roots.

Give Rise to

Apical Meristem: The apical meristem gives rise to the epidermis, xylem, phloem, and ground tissue.

Lateral Meristem: The lateral meristem gives rise to wood, inner bark, and outer bark.

Consist of

Apical Meristem: The apical meristem consists of protoderm, procambium, and ground meristem.

Lateral Meristem: The lateral meristem consists of vascular cambium and cork cambium.

Function

Apical Meristem: The apical meristem allows the plant to develop special structures like flowers and leaves.

Lateral Meristem: The lateral meristem allows the plant to grow tall by making it stronger.

Occurrence

Apical Meristem: The apical meristem occurs in all phyla of plants.

Lateral Meristem: The lateral meristem is absent in mosses and horsetails.

Conclusion

Apical meristem and lateral meristem are two types of meristematic tissue that are responsible for the growth of a plant. Both meristems consist of undifferentiated cells which are capable of actively dividing. The apical meristem occurs in the apex of the stem and roots. It is responsible for the primary growth of the plant that increases the length of the plant from its apices. The lateral meristem lies laterally in the stem and roots. It is responsible for the secondary growth of the plant. Vascular cambium and cork cambium are involved in increasing the diameter of stem and roots. Thus, the main difference between apical and lateral meristem is in their position and the function in the plant.

 Reference:
1. “Apical Meristem: Definition & Function.” Study.com. N.p., n.d. Web. 25 May 2017. <http://study.com/academy/lesson/apical-meristem-definition-function-quiz.html>.
2. “Types of Meristems.” NGA’s LEARNING Garden. N.p., n.d. Web. 25 May 2017. <https://garden.org/courseweb/course1/week1/page16b.htm>.

Image Courtesy:
1. “Coleus stemtip L” By Jon Houseman – Jon Houseman and Matthew Ford (CC BY-SA 4.0) via Commons Wikimedia
2. “Tree secondary components diagram” By Brer Lappin – Own work (Public Domain) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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