PATTERNS IN STEM ELONGATION RATE IN CHRYSANTHEMUM AND TOMATO PLANTS IN RELATION TO IRRADIANCE AND DAY-NIGHT TEMPERATURE

Stem elongation of young plants of Lycopersicon esculentum Mill. 'Mata dor' and Dendranthema morifolia Ramat. 'Choral Charm' was continuously measured under greenhouse conditions with a high degree of resolution , using linear voltage differential transducers. High stem elongation rate (SER) during the night and low SER during the day was found in bo th species. During the day the SER was correlated with, and quickly ad apted to, the irradiance. High irradiance during the day induced high SER during the following night. Furthermore, several SER maxima were f ound during the night, with a different distribution in the two specie s. Plants grown under a negative day/night temperature programme (low day/ high night temperature) had a lower SER during the night and day than plants grown at constant temperature.