Figure 3.

Role of xylem calcium in vulnerability to cavitation in different woody species. For each species, stems were perfused with NaPO₄ solutions at pH 4 or pH 10, and the P₅₀ values were scored. Each dot represents the data for one angiosperm species (black symbols) or for one coniferophyte species (white symbols). The top section (A) shows P₅₀ values at pH 4 versus P₅₀ values at pH 10. The bottom section (B) shows the P₅₀ values at pH 4 versus the shift in P₅₀ values calculated as P_{50 pH4} − P_{50 pH10}. Data are means (±se) of three to four samples. The solid line is a regression on the mean values, with r² = 0.88 and P_{50 pH4} − P_{50 pH10} = 0.707 P_{50 pH4} + 1.055 (P < 0. 001). The dashed line is the function P_{50 pH4} = P_{50 pH10}.