Plants are able to assess their environment by analyzing light, and are able to "remember" light they have experienced recently. By analyzing chemical reactions in leaves, scientists have come to appreciate that plants possess a kind of intelligence.

BBC News has a terrific story on a group of researchers who believe they have found the plant equivalent of the nervous system, which functions by translating light into chemical reactions - and remembering those reactions over time. Plants need to analyze and remember different wavelengths of light in order to prepare for seasonal variations in pests and pathogens in the air.

According to BBC News:

What was even more peculiar, Professor [Stanislaw] Karpinski said, was that the plants' responses changed depending on the colour of the light that was being shone on them. There were characteristic [changes] for red, blue and white light," he explained.

He suspected that the plants might use the information encoded in the light to stimulate protective chemical reactions. He and his colleagues examined this more closely by looking at the effect of different colours of light on the plants' immunity to disease.

"When we shone the light for on the plant for one hour and then infected it [with a virus or with bacteria] 24 hours after that light exposure, it resisted the infection," he explained.

"But when we infected the plant before shining the light, it could not build up resistance.

"[So the plant] has a specific memory for the light which builds its immunity against pathogens, and it can adjust to varying light conditions."

He said that plants used information encrypted in the light to immunise themselves against seasonal pathogens.

"Every day or week of the season has… a characteristic light quality," Professor Karpinski explained. "So the plants perform a sort of biological light computation, using information contained in the light to immunise themselves against diseases that are prevalent during that season."

Professor Christine Foyer, a plant scientist from the University of Leeds, said the study "took our thinking one step forward".

"Plants have to survive stresses, such as drought or cold, and live through it and keep growing," she told BBC News.

"This requires an appraisal of the situation and an appropriate response - that's a form of intelligence."