The girth of stem increases due to ---.

(a) Apical meristem

(b) Lateral meristem

(c) Intercalary meristem

(d) All of the above

The girth of a stem increases primarily due to the activity of the lateral meristem. So, the correct answer to your question is (b) Lateral meristem. Let’s delve deeper into why this is the case and how different types of meristems contribute to plant growth.

Understanding Meristems

Meristems are regions in plants where cells are actively dividing, leading to growth. There are three main types of meristems: apical, lateral, and intercalary. Each serves a distinct purpose in the plant's development.

Types of Meristems

• Apical Meristem: Located at the tips of roots and shoots, apical meristems are responsible for the primary growth of the plant, which increases its height and length.
• Lateral Meristem: Found in the vascular and cork cambium, lateral meristems are crucial for secondary growth. They contribute to the increase in girth or thickness of the stem and roots.
• Intercalary Meristem: These are found at the base of leaves and internodes in some plants, like grasses. They allow for rapid growth and elongation of these parts but do not significantly contribute to the girth.

The Role of Lateral Meristem in Girth Increase

When we talk about the increase in girth, we are specifically referring to secondary growth, which is primarily facilitated by lateral meristems. The lateral meristem consists of two main types:

• Vascular Cambium: This layer produces new xylem (wood) and phloem (bark), contributing to the thickness of the stem.
• Cork Cambium: This layer produces cork cells, which form the outer protective layer of the stem.

As these meristems divide and produce new cells, the stem expands in diameter, allowing the plant to support more weight and transport nutrients more efficiently.

Examples in Nature

Consider a tree, which exhibits significant secondary growth. The trunk becomes thicker over the years due to the activity of the lateral meristem. In contrast, a young plant primarily grows taller due to the apical meristem, but as it matures, the lateral meristem takes over to increase girth.

Conclusion

In summary, while all types of meristems play vital roles in plant growth, the lateral meristem is specifically responsible for increasing the girth of stems. Understanding these different meristems helps us appreciate how plants adapt and grow in their environments.