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No. 116: Mar-Apr 1998

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Eyeless Vision

Tomatoes see red. And other colors, too! We touched on this subject over a decade ago. (SF#54) Then we described how the use of red plastic mulch greatly improves the yields of tomato plants. More recent research reveals that fruit quality and resistance to pests are also improved. How can this be?

Plant leaves, it turns out, contain color sensors -- light-sensitive pigments similar to those it the human retina. Obviously, the plants do not "see," but the pigments provide environmental information. Here's the mechanism: plant leaves reflect infrared light well, so when a tomato plant's pigments detect a lot of infrared, the plant "thinks" that it may be crowded out by competing vegetation. The tomato plant responds aggressively by growing more rapidly.

The red plastic mulch between the rows also reflects a lot of infrared light, and it thereby tricks the tomato plant into accelerating its growth.

(Raloff, Janet; "When Tomatoes See Red," Science News, 152:376, 1997.)

Fire-detecting beetles. The beetle Melanophila acuminata seeks out forests that have just been ravaged by fires so that it can lay its eggs in the nutritious, freshly burnt wood. These insects are capable of detecting fires up to 32 kilometers (20 miles) distant. They do not see the fire with their eyes but instead detect the thermal (infrared) radiation with a special organ on their chests.

(Schmitz, Helmut, et al; "Infrared Detection in a Beetle," Nature, 386:773, 1997.)

Knees "see". Well, sort of, and then only the backs of the knees. Human circadian clocks can be shifted by shining visible light on the skin on the backs of the knees. It is theorized that the light penetrates the skin and causes chemical changes in the blood, implying that human blood contains "chronobiological photoreceptors."

(Oren, Dan A., and Terman, Michael; "Tweaking the Human Circadian Clock with Light," Science, 279:333, 1998. Also: Campbell, Scott S., and Murphy, Patricia J.; "Extraocular Circadian Phototransduction in Humans," Science, 279:396, 1998.)

Comment. We can see how the tomatoes and beetles might find exotic photoreceptors useful, but what environmental pressures would favor the evolution of photoreceptors in the human blood?

Our circadian clock can be reset by light through the eyes or light shining on the backs of knees. Our circadian clock can be reset by light through the eyes or light shining on the backs of knees.

From Science Frontiers #116, MAR-APR 1998. 1998-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:


  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987