Is xylem of angiosperm leaves less resistant to embolism than branches? Insights from microCT, hydraulics, and anatomy.

According to the hydraulic vulnerability segmentation hypothesis, leaves are more vulnerable to decline of hydraulic conductivity than branches, but whether stem xylem is more embolism resistant than leaves remains unclear. Drought-induced embolism resistance of leaf xylem was investigated based on X-ray microcomputed tomography (microCT) for Betula pendula, Laurus nobilis, and Liriodendron tulipifera, excluding outside-xylem, and compared with hydraulic vulnerability curves for branch xylem. Moreover, bordered pit characters related to embolism resistance were investigated for both organs. Theoretical P50 values (i.e. the xylem pressure corresponding to 50% loss of hydraulic conductance) of leaves were generally within the same range as hydraulic P50 values of branches. P50 values of leaves were similar to branches for L. tulipifera (-2.01 versus -2.10 MPa, respectively), more negative for B. pendula (-2.87 versus -1.80 MPa), and less negative for L. nobilis (-6.4 versus -9.2 MPa). Despite more narrow conduits in leaves than branches, mean interconduit pit membrane thickness was similar in both organs, but significantly higher in leaves of B. pendula than in branches. This case study indicates that xylem shows a largely similar embolism resistance across leaves and branches, although differences both within and across organs may occur, suggesting interspecific variation with regard to the hydraulic vulnerability segmentation hypothesis.

Which Bay Leaf is in Your Spice Rack? - A Quality Control Study.

The accurate identification of bay leaf in natural products commerce may often be confusing as the name is applied to several different species of aromatic plants. The true "bay leaf", also known as "bay laurel" or "sweet bay", is sourced from the tree Laurus nobilis, a native of the Mediterranean region. Nevertheless, the leaves of several other species including Cinnamomum tamala, Litsea glaucescens, Pimenta racemosa, Syzygium polyanthum, and Umbellularia californica are commonly substituted or mistaken for true bay leaves due to their similarity in the leaf morphology, aroma, and flavor. Substitute species are, however, often sold as "bay leaves". As such, the name "bay leaf" in literature and herbal commerce may refer to any of these botanicals. The odor and flavor of these leaves are, however, not the same as the true bay leaf, and for that reason they should not be used in cooking as a substitute for L. nobilis. Some of the bay leaf substitutes can also cause potential health problems. Therefore, the correct identification of the true bay leaf is important. The present work provides a detailed comparative study of the leaf morphological and anatomical features of L. nobilis and its common surrogates to allow for correct identification.