Caffeine crystals by Annie Cavanagh and David McCarthy. This false-coloured scanning electron micrograph shows caffeine crystals. Caffeine is a bitter, crystalline xanthine alkaloid that acts as a stimulant drug.
Not to be sneezed at! Microscopic images reveal the invisible enemies faced by hayfever sufferers
Nakaya photographed thousands of snow crystals. Studying these photographs allowed him to develop a systematic classification system for snowflakes. In the end, he defined 41 individual morphological types. Above, a fernlike stellar dendrite.