Figure 5.6 Whole mount of a cleared leaf of Eucalyptus crenulata showing the more complicated arrangement of supply and distribution veins characteristic of a dicotyledonous leaf. Islands marked out by large veins with large vessels, in which water is moved rapidly all over the lamina, surround islets of small veins with small vessels in which water is slowly distributed locally to the mesophyll. The ratio of small to large veins in a dicotyleclonous leaf is much larger than in a grass leaf (see Figure 5.4). A factor of 10 is not uncommon, suggesting that c. 90% of evaporated water comes from the small veins. Partial phase-contrast optics. Scale bar = 1 mm (Photograph courtesy M. McCully and M. Canny)