Collenchyma is found in epidermis of dicot stem and petioles and abundant in climbing stems.It is a living mechanical tissue which provides both mechanical strength and elasticity and allow them to grow in size

In order to explain why collenchyma occurs in the stem and petioles of dicot herbs, let's first understand what collenchyma tissue is and its role in plants.

What is collenchyma tissue?
Collenchyma is a type of simple permanent tissue found in plants. It is characterized by cells that have thickened cell walls, primarily composed of cellulose, hemicellulose, and pectin. These thickened cell walls provide mechanical support and flexibility to the plant.

Role of collenchyma tissue
Collenchyma tissue plays a vital role in providing mechanical support to the growing parts of plants, such as stems and petioles. It helps in maintaining the structural integrity of these organs and prevents them from collapsing under the weight of leaves and other parts. Additionally, collenchyma tissue also allows for flexibility and bending, enabling the plant to adapt to various environmental conditions, such as wind or mechanical stress.

Occurrence of collenchyma in dicot herbs
Dicot herbs are a group of plants that belong to the class Dicotyledonae. They are characterized by having two cotyledons and a branched network of veins in their leaves. Collenchyma tissue is commonly found in the stems and petioles of dicot herbs, and there are several reasons for this occurrence.

1. Mechanical support: The stems and petioles of dicot herbs need to provide support to the leaves and flowers, preventing them from drooping or bending. Collenchyma tissue, with its thickened cell walls, provides the necessary mechanical strength to withstand these forces.

2. Flexibility: Dicot herbs often experience bending or swaying due to external factors like wind or touch. The presence of collenchyma tissue allows these organs to flex and bend without breaking, reducing the risk of damage.

3. Growth and development: Dicot herbs typically undergo active growth and development, especially during their early stages. Collenchyma tissue aids in the elongation and expansion of stems and petioles, accommodating the increasing size of leaves and flowers.

Conclusion
In conclusion, collenchyma tissue occurs in the stem and petioles of dicot herbs due to its role in providing mechanical support, flexibility, and facilitating growth and development. This tissue's thickened cell walls give strength and prevent collapse, allowing the plant to thrive in various environmental conditions.