Correction

ECOLOGY. For the article “Surface gas-exchange processes of snow algae,” by William E. Williams, Holly L. Gorton, and Thomas C. Vogelmann, which appeared in number 2, January 21, 2003, of Proc. Natl. Acad. Sci. USA (100, 562–566; First Published January 7, 2003; 10.1073/pnas.0235560100), on page 565, right column, second paragraph, in the sentences beginning on the 11th line, the personal communication was presented incorrectly. The sentences reading “Recent reanalysis of their data suggests that the number should be closer to 300 cells ml⁻¹ (T. H. Painter, personal communication). Their assumption that all of the cells are in the top 10 cm of snow would give an average areal density of 3 × 10⁷ cells m⁻²” should be replaced by “They assumed that all of the cells were in the top 10 cm of snow but now believe it is more appropriate to assume they are in the top 2 cm (T. H. Painter, personal communication). Using this assumption gives an average areal density about 3 × 10⁷ cells m⁻².” This correction does not affect the conclusions of the article.