HYDRATION, PHOTOSYNTHESIS AND RESPIRATION 227 



were kept for 24 hours in a saturated atmosphere and then placed in a small 

 air-conditioned chamber of the following inner dimensions : 3 5 cm X 3 5 cm 

 X40 cm. The chamber was flushed with temperature- and humidity- 

 conditioned air with the normal concentration of carbon dioxide (i.e. 

 about 055 mg CO2/1000 ml). The air in the chamber had a temperature of 

 25 + o-2°C, relative humidity of 80 ±3%. The plant in the chamber was 

 illuminated from above with five incandescent bulbs, Tungsraphot B 500 

 W, and with four Philora 75 W Phillips, through a continuous-flow water 

 filter 8 cm in height, the total constant intensity being 40,000 lux (with 

 stabihsed mains voltage). For the experiments mature leaves of the central 

 insertion level were used in situ (on the plant), the apex and the base of the 

 leaf being covered bilaterally with leaf chambers provided with plexite 

 windows (photograph in Catsky, i960) which enclosed an area of 12 cm 2. 

 Experimental air was drawn through these horizontally placed leaf cham- 

 bers by means of membrane pumps at the constant rate of 10 1/hr, passing 

 then into an infrared COa-analyser (Infralyt, Dessau, Germany). This 

 analyser with a selective condenser detector was set up in a differential 

 circuit so that it measured directly the difference in concentration between 

 the experimental and control air. The measuring tube of the analyser was 

 alternately connected with the basal and apical leaf chamber placed on the 

 same leaf Control air was passed through the reference tube. A 50 ^A 

 recorder registered values which, during constant flow of experimental 

 air, were directly proportional to the intensity of photosynthesis of the 

 part of the leaf-blade enclosed in the leaf chamber. Sufficient rate of air 

 flow with a very small leaf-chamber volume ensured that no excessive 

 heating of the leaves occurred and that even at the highest intensities of 

 photosynthesis the concentration of carbon dioxide never dropped by 

 more than 20%. A second control infrared analyser measured the con- 

 centration of CO 2 in the control air. For details see Slavik and Catsky 

 (1961). The values of intensity of photosynthesis were expressed as mg 

 COg/dm^/hr. 



When the intensity of respiration was measured higher accuracy was 

 achieved by using the conventional manometric estimation according to 

 Warburg. Each manometric flask contained 6 leaf discs of 15 mm in dia- 

 meter cut out either from the apical or from the basal part of the leaf-blade 

 (circles in Fig. i). Experimental leaves were chosen on the basis of criteria 

 common to analogous experimental plants as used for estimation of 

 photosynthesis and were also saturated with water prior to the experiment. 



The side-arm of the flask contained i ml/ water which ensured minimum 

 transpiration loss from the leaf tissue discs during measurement. The esti- 



