A method of monitoring health in chlorophyll containing matter comprises exposing the matter to a light source to cause chlorophyll to fluoresce and emit a fluorescence signal. Any changes in a parameter indicative of changes in the intensity of the fluorescence signal are detected and compared with a predetermined threshold. A change which exceeds the predetermined threshold is interpreted as a transition of the level of stress in the chlorophyll containing matter. An apparatus for monitoring health in chlorophyll containing matter is also provided and comprises a light source for causing chlorophyll in the matter to fluoresce, a detector for detecting the intensity the fluorescent signal, means for measuring changes in a parameter indicative of changes in the intensity of the fluorescent signal and a detector to detect an increase in the change of the parameter above a predetermined threshold.