Leaf Movements: Rosetta Stone of Plant Behavior?

Abstract

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Several families of plants have representatives whose leaves move in a regular and predictable pattern during day and night. Generally, the leaf sur-faces are horizontal and face the sun. during the day, then fold together in a vertical position at sunset. This process, referred to as nyctinasty (night move-ment), was described more than 2,300 years ago by Androsthenes, who noted nyctinastic legumes during the march of Alexander the Great. Charles Darwin, fascinated by these movements, hypo-thesized that nyctinasty provides protection against thermal radiation, since vertical leaves facing each other lose less heat at night than do horizontal leaves facing the open sky (Darwin 1881). Biinning and Moser (1969) wondered why bright moonlight did not disturb photoperiodic time measurement in short-day species, which require a long uninterrupted dark period for floral initiation. They noted that many short-day plants have nyctinastic leaves and that leaves cannot absorb light from the zenith efficiently when in the night position. After careful measurements, they concluded that nyctinastic move-ment reduces the absorption of moon-light below threshold intensity for inter-fering with floral induction, and ac-cordingly concluded that protection of photoperiodic time measurement was the main function of nyctinasty under natural conditions. Neither of these