Enhanced image of a cross-section of a pine stem
© Garry DeLong/Getty Images
Enhanced image of a cross-section of a pine stem
This enhanced image of a cross-section of pine stem shows the growth of the plant’s inner and outer tissues. It also demonstrates how frequently circles appear in the natural world, as the growth of the pine pushes out nearly equally from the centre point. It’s not a perfect circle, but you could calculate the circumference of this stem by using the mathematical constant we call ‘pi’.
Why call out pi? Because today is Pi Day, an observance that’s been around since at least 1988, when the staff of the San Francisco Exploratorium first organised a march to celebrate the date of March 14, which is written 3/14 in the United States. That's an approximation of 3.14, the first three digits of pi.
Related Images
Illuminated icicles in Chichibu, Japan
A European goldfinch perched among rosehips in snow
Ocean Drive in Miami, Florida
Members of the Wild Red Flame Mardi Gras Indians in New Orleans, Louisiana
The Harbin Ice and Snow Festival in China
Grey-crowned cranes forming a heart shape
Ruff male displaying on Varanger Peninsula in Norway
Aerial shot of mangroves at King Sound, Western Australia
Bing Today Images
Mute swan with chicks, Hesse, Germany
Mar 13, 2026
Gran Paradiso National Park, Piedmont, Italy
Mar 13, 2025
Lesser flamingos flying over Lake Magadi, Kenya
Mar 13, 2024
European hare, Netherlands
Mar 13, 2022
The Circle Bridge in Copenhagen, Denmark
Mar 13, 2020
