Colour scanning electron microscopy of peltate glandular trichomes of fresh developing hops (Humulus lupulus L.]

Morphological and colour changes of fresh developing hop female cones were examined using a colour scanning electron microscopy technique. A highlight component of a video microscope image was replaced with the counterpart of an SEM image by digital image processing for better resolution. In order to obtain colour information specific to specimen surfaces, the SEM observation was carried out under low vacuum (similar to 50 Pa) and at a low temperature (-20 degrees C) without conventional specimen preparations. It was found that the bottom cuticular surface of the cup-shaped trichomes gradually upheaved and their colour turned yellow, as the cones grew.