Introduction

Water is an essential component for a land plant to survive. While watering the plants, have you ever noticed that the water droplets on the leaves of some plant species form small spheres and slide off? This is a fascinating phenomenon and is the result of a combination of factors that affect the physical properties of the leaf surface. In this article, we will explore why water rolls off the leaves of land plants.

Leaf Surface Structure

The surface of the leaf of a land plant is not smooth; it is composed of ridges and grooves. The ridges form a sub-micron structure that provides a large surface area. This creates a superhydrophobic surface that causes water to bead up and roll off the leaf. The sub-micron structure of the leaf surface is called the epicuticular wax layer, which plays a key role in repelling water.

Role of Epicuticular Wax Layer

The epicuticular wax layer is a thin, waxy coating on the surface of the leaf that acts as a barrier to water. It is composed of hydrophobic compounds, which are water-repelling molecules. The wax layer is composed of different compounds in different plant species. For example, in some plants, it is composed of fatty acid derivatives, while in others, it is made up of alkanes or terpenes. The wax layer protects the leaves from water loss due to transpiration and also protects against microbial and fungal attacks.

Contact Angle

Contact angle is a measure of how much a droplet of liquid adheres to the surface. When a droplet of water is placed on a surface of a leaf, it forms a particular contact angle with the surface. If the angle is greater than 90 degrees, the surface is hydrophobic, and the droplet will roll off. A contact angle of less than 90 degrees means that the surface is hydrophilic, and the droplet will spread out on the surface.

Surface Tension

Surface tension is another factor that determines how water behaves on a surface. The water droplet on the leaf surface minimizes its surface area by forming a sphere. The surface tension of water is strong enough to hold the droplet together in the shape of a sphere. As a result, the droplet slides off the surface of the leaf.

Conclusion

In conclusion, the leaves of land plants have a hydrophobic and superhydrophobic surface due to the presence of the epicuticular wax layer. This layer plays a critical role in repelling water and protecting the leaf from water loss and microbial attacks. The combination of contact angle and surface tension is responsible for the formation of water droplets on the leaf surface and their rolling off. Understanding the physical properties of the leaf surface and how it repels water could have promising applications in the engineering world, where superhydrophobic surfaces could be used to create self-cleaning surfaces or anti-corrosion coatings.