Carob Tree

August 29, 2013

Carob tree green pods1

Photographer: Menashe Davidson
Summary Author: Menashe Davidson

The photo at top shows a stand of Carob trees (Ceratonia siliqua) in Rishon LeZion, central Israel. The Carob is an evergreen tree of the Fabaceae family, native to the Mediterranean region, used extensively for agriculture but can be found growing wild. Planting carob seeds dates back to Mesopotamian culture. The tree fruit (most carob trees are dioecious) is a pod. Each contains about 10 seeds per pod -- inset photo. The seeds are quite similar and have almost the same weight, about 200 milligrams (0.2 grams -- 1 gram equals 0.035 ounce) per seed.

Carob Tree insetIt's believed that "carat," the unit by which precious metal and stone weight is measured, was derived from carob seeds since they have unusually low variability in their mass. An ancient practice of people in the Middle East was to weigh gold and gemstones against the seeds of the carob tree. Later, the system was eventually standardized and one carat was fixed at 200 milligrams.

Biking among carob trees in a park in Rishon LeZion, I recalled the linkage between the carob tree and the carat unit. I decided to check to see if, in fact, the seed weight approximated the standardized carat weight. So, I collected dry pods from the ground, took 60 seeds at random, and weighed them on a very accurate pharmacy scale. The average weight per seed was 210 milligrams with very little deviation. Marvelous!  Top photo taken on May 17, 2013.

Photo details: Top - Camera Model: NIKON D80; Focal Length: 40mm (35mm equivalent: 60mm); Aperture: f/10.0; Exposure Time: 0.010 s (1/100); ISO equiv: 200. Inset - Same except Focal Length: 135.0mm (35mm equivalent: 202mm); Aperture: f/8.0; ISO equiv: 400.