Instant cold-hardiness is a characteristic common to all species of fungi that grow in the Arctic. Periodic hard frosts in mid-summer make it imperative for polar fungi to be able to resume growth immediately in the brief growing season. Thus, Arctic fungi have evolved spores that are resistant to many environmental extremes, including freezing, starvation, and dessication. To survive low temperatures, fungi produce substances – glycerol, proline, and trehalose – which act as cryoprotectants. These solutes allow fungi to grow at temperatures as low as -5°C, protecting hyphal cells from potentially lethal shrinkage and ice crystal formation.