image credit: Eleni Katifori; image source; additional image

Why Leaves Aren't Trees

This is a lemon leaf that was wounded to interfere with its circulation. Note how the network of veins enabled nutrients to flow beyond the wound.

- Click on the image to see a similar experiment with a ginkgo leaf.
- To learn about the controversy over how these different vein structures developed, see Why Leaves Aren't Trees.

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Konigsberg Bridge

If you enjoy solving puzzles, try the seven bridges challenge.
- This problem helped lead the mathematician Leonhard Euler to develop new mathematical fields, graph theory and topology. See Konigsberg Bridge to learn more.
- Also see the Wikipedia page for variations on this problem.

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image credit: Cesar Hidalgo; image source; larger image

Network Theory: A Key to Unraveling How Nature Works

You are looking at a network diagram that shows the interconnectedness of the world economy. To learn more about this network, visit Mapping the World Economy.

- To find out how networks are related to "Six Degrees of Kevin Bacon," visit Network Theory: A Key to Unraveling How Nature Works.
- To learn about a physicist who studies networks, see Physics Rules Network Dynamics.

Four Color Theorem Intro

Have you ever wondered how many colors are necessary to make a map? Four Color Theorem Intro can help you figure it out!

- To learn more see this page by Ivars Peterson.