Plants can be observed methodically year after year and dates can be recorded when certain distinguishable growth stages, such as opening of leaf buds or appearance of first flowers, occur. These plants may be considered as special, highly sensitive meteorological instruments that integrate the composite effect of weather factors such as temperature, rainfall, humidity, wind, and sunshine in their growth response. Using indicator plants that are genetically alike and observing them at numerous locations creates a network that supplements the cooperative weather observations of the National Weather Service. From the annual phenological reports, average dates for certain events can be established. Data can then be related to these averages for purposes of monitoring and characterizing individual seasons.