Scanning Electron Micrograph (SEM) of a cross-fractured leaf of Vicia faba (broad bean), showing a uredium of the fungus Uromyces viciae-fabae (Faba-bean rust). It has developed as an erumpent, initially subepidermal pustule on the adaxial surface of the leaf. Urediospores at various stages of development can be seen; the mature ones attached to their pedicles at the top of the uredium. Intercellular hyphae grow between the palisade and spongy mesophyll cells. Magnification: 650X at 8x10" print size.