A gas perfusion microcalorimetric system has been developed for metabo
lic investigations of plant tissues under dark conditions, The system
consists of two twin heat conduction microcalorimeters connected by ga
s-tight tubing. During measurements, a flow of humid gas enters the ma
in calorimeter containing the plant tissue. The volume of this sample
chamber can be varied between 4 and 25 ml and the flow rate of the gas
can be varied up to maximum of 150 ml h(-1). The outgoing air is allo
wed to pass through a second calorimeter, serving as an on-line CO2 an
alyzer. Gases, such as NOx or CO2, can be added to the incoming gas-fl
ow either continuously or by stepwise injection. The calorimetric syst
em has been tested in respiratory experiments with potato tuber slices
.