Exodermis An outermost layer of thickened or suberized cortical cells that sometimes replaces the epidermal layer in the older parts of roots if the epidermal cells have died.
This heating helps to break down weak spots in the dielectric that otherwise might pass through the electrode undetected, only to fail during a later spark or hipot test.
In 1895, Wilhelm Roentgen accidentally discovered that a cathode-ray tube could make a sheet of paper coated with barium platinocyanide glow, even when the tube and the paper were in separate rooms.