(a) Traditional rehydration survival test results. Plants were subjected to drought treatment for 20 days, after which watering was resumed; values indicate the number of plants that recovered within 3 days of rehydration. For each line, n = 7. (b) Threshold survival test results. For control populations, n = 2 for each line; for drought-treated populations, n = 13 for each line. s.d. = standard deviation. Pairwise t-tests were performed against survival times of wild-type Columbia plants, yielding p-values as shown; n.s. = not significant.