Nanoparticle localization inside the xylem vessels. A) Phase contrast image of a vascular core, showing a cluster of dark bright dense material inside of a xylem vessel. B) TEM image of the vessel containing the dense material in an ultrathin consecutive section. C) Detail of the region indicated in (B)(*), showing presence of nanoparticles in the electron dense material. Bar in A and B = 30 μm; C = 500 nm.