Figure 4.

Lignification and P₅₀. A to C, Cross sections of hollow stems through the internodes of the grasses Phalaris arundinacea (A; P₅₀ = −0.5 MPa), L. perenne (B; P₅₀ = −4.6 MPa), and Brachypodium pinnatum (C; P₅₀ = −6.2 MPa), showing more lignification in the outer zones of the stems (arrows) and thicker-walled fibers (insets) with increasing P₅₀. D and E, Grasses and herbaceous eudicots that are more resistant to embolism have a higher proportion of lignified tissues in their stems (D) and thicker-walled fibers (E). Error bars show se (only lower limits are presented for clarity purposes, and each point represents the average value for three specimens of the same species). Marked zones apply to the 95% confidence limit of the regression. See Supplemental Table S6 for multiple regression analysis of P₅₀ and anatomical features as predictive variables.