In figure 1 CO₂-changes over 24h and measured at different times during the culture period of in vitro roses are presented. During the dark period the CO₂-concentration is build up due to respiration and rather high concentrations are measured. In the light the concentration decreases more or less exponentially. As the culture period extends, a more distinct pattern, reaching higher CO₂-levels, is obtained. Notice also that between different culture vessels a rather high variation in CO₂-concentration is measured.