RELATIVE HUMIDITY
Relative humidity is the ratio of actual vapor
pressure of water vapor in the air to the vapor
pressure that would be present if the air was
saturated with moisture at the same temperature.
Water vapor moves from one location to another
because of vapor pressure differences, so relative
humidity affects transpiration from plants by
affecting the vapor pressure difference between a
plant leaf and surrounding air. Normal plant growth
will generally occur at relative humidities between
25–80%. A secondary effect of relative humidity is
the response of pathogenic organisms. For example,
most pathogenic spores will not germinate at
relative humidities below 95%.