Lacy Leaves

The vein structure of leaves serves as an amazing and flexible distribution system.

What kind of organism would you say is most successful on our planet? How about plants?

Plants are everywhere: there are houseplants, ornamental plants, vegetables, fruits, and plants in the forest and meadows. Practically every inch of land on Earth is covered by plants, and small microscopic plants float in the oceans and lakes as well. What makes plants so successful? One thing many plants have in common is leaves, an important structure that contributes to their success.

This activity explores leaves using their vein structure. To make it more engaging, you can make double frames of cardboard (approx. 5x7 cm), so the students can place their leaves into the frame.

1. Ask pupils to gather leaves of trees (or other dicot plants) – best to do this activity in a forest, but the schoolyard may also work fine. Each pupil should select one leaf and place it into their frame. Encourage them to find different leaves; in this case they can see more vein systems.
2. Ask them to stand in a circle and keep their 'slide' towards the sun to examine the vein system of their leaf. Then, ask them to pass their 'slide' to the right, and examine their neighbour’s leaf. You can continue until pupils receive their original leaf back.
3. After looking, ask pupils to examine their leaves with a magnifying lens. They can also can trace the leaf onto paper and find routes along the veins connecting up different parts of the leaf, illustrating how everything is connected. This activity can be done inside or outside, with the help of a clipboard. You might ask pupils:

• Can you trace a route along the veins from the middle to the edge of your leaf?
• Can you find different routes to the same place?
• What might this mean for the leaf if part of it becomes damaged?
• How could we use this property (more than one route for transportation) of the vein system? Think also about delivering utilities such as water, gas, and electricity.

By examining the leaf vein structure, you can see the main vein (midrib) and the smaller ones (primary veins) and the even smaller ones (secondary veins).  Why is it like this?

Simple explanation

Water needs to get to all of the cells of the leaf. The leaf veins create a system with many interconnections. This means that liquids can flow to the same cell via different routes. This is helpful in case the leaf is damaged, for example by a caterpillar. In this case the liquids can follow a different route to travel and the leaf can keep functioning. We call this system of interconnected pathways redundancy.

More detailed explanation

This kind of distribution system continues working not only if damaged. When there is a lot of water, all the pathways are used, when less, only some of them. Note, not only water needs to be transported, but also the food produced by leaves (mainly liquid sugar) needs to reach all parts of the plant.

And what about monocot plants? They have a parallel vein system, so how can they reach all the cells? You can examine this as well. The parallel veins are connected.

The table below outlines the differences between monocot and dicot plants, illustrated above.

We can learn from the vein system of leaves how to make resilient distribution systems. A resilient distribution system still works even if damaged. In this case, there is more than one way to move goods from a to b. This system can be mimicked in distribution systems including transportation, water or electricity. These can all be designed to have nested and interconnected loops. For example, electricity supply lines become more resilient when there are multiple routes for the electricity to flow. Trees can fall and damage electricity lines, but with alternative routes the electricity can still reach where it is needed. The operation of such systems are more sustainable and reduces the risk of loss of supply if damaged. These kinds of systems are more expensive to build initially, but over time, these systems are often less expensive since they require repair less often and keep everything relying on this infrastructure functioning.

Not only the vein system of leaves has this kind of distribution. You can find similar loopy networks in the structural veins of insect wings (you can observe it on dragonfly wings), in the architecture of some corals, in the blood vessels of the brain or retina, in the net of mycelium in the soil.

Some STEAM opportunities include:

• Observing and raising questions about how different plants adapt.
• Analyse advantage and disadvantage of different adaptations/behaviours.

• What other distribution systems do you know in nature? Are they similar to the one in the leaf’s vein system or different?
• Where do humans use distribution systems?
• Can you think of examples where the lessons from leaves might be useful?

Vein systems in leaves are more resilient (find out more).

Leaves are being used as inspiration for new distriution networks (find out more).

Loops are common in natural networks and increase strength (find out more).