Light quality and sun tracking in Malva neglecta

Two distinct spectral components were found to be necessary to produce solar-tracking movements of the leaves of Malva neglecta: a small blue vectorial component with a quantum flux as low as 10 μmol∙m−2∙s−1 was found to be sufficient to determine the direction of movement, but responses do not take place unless additional radiation (regardless of spectral quality or direction) raise the total photosynthetically active component above the current light compensation point (70 μmol∙m−2∙s−1). This additional radiation could be given simultaneously or in an immediately preceding light treatment.