Depletion of the ozone layer is of concern because the stratospheric ozone column is the primary attenuator of solar ultraviolet-B radiation (UV-B region, between 290 and 320 nm). A decrease in this ozone column would lead to increases in UV-B reaching the earth's surface. Ultraviolet-B radiation comprises only a small portion of the electromagnetic spectrum but has a disproportionately large photobiological effect. Both plants and animals are greatly affected by increases in UV-B radiation but there exists tremendous variability in the sensitivity of plant species to UV-B radiation. Approximately two out of three species tested appear sensitive and sensitivity also differs among cultivars of the same species. Plants have developed natural adaptations such as anatomical, morphological and biochemical changes which protect them from UV-B radiation. The extent of these natural adaptations may be related to the geographic origin of the species. It has been hypothesized that species originating from areas which receive high levels of UV-B radiation would be highly resistant to UV-B radiation. Plants collected along a 3000 m elevational gradient in Hawaii showed differences in sensitivity which were correlated with elevation. Most plants native to low elevations were sensitive to UV-B, but plants from the higher elevations, where UV-B is greatest, were very tolerant to UV-B radiation.