Guttation

Day 361: "Why is that plant/fungus sweating?" Particularly while hiking in the early morning hours, you may have noticed someting resembling dew on the margins of leaves, at the tips of blades of grass or sometimes on flower petals even though dew is not otherwise in evidence. In plants, this occurs when soil moisture is high and the plant's uptake of water exceeds its rate of traspiration due to its stomata ("breathing pores") being closed at night. Root pressure forces the excess out through specialized sructures called hydathodes. The process is less fully understood as it applies to fungi, but some theorize that it is the mushroom's way of protecting itself against rot, expelling excess moisture from its internal tissues. The photo above shows guttation droplets on a crust fungus.