NUANCED DISCRIMINATION. “Many signals modify the plant phenotype. Many abiotic signals are sensed by plants. For example, humidity, light, minerals, gravity, wind, snow melt, soil structure and composition, etc., and totaling about 20 in number, initiate phenotypic changes. Furthermore these signals are sensed and the intensity, the direction and the length of exposure are finely discriminated.”
http://link.springer.com/article/10.1007/s00114-005-0014-9