HYDRATION, PHOTOSYNTHESIS AND RESPIRATION 231 



comparison with the observed differences in the intensity of photosynthesis 

 to explain them. 



As concerns the opening width of the stomata, it should be mentioned at 

 this point that in the present paper the intensities of photosynthesis are 

 compared during the steady initial phase of measurement when no decrease 

 takes place which could be ascribed to hydroactive closing of the stomata. 

 As was mentioned above, any possible (but not observed here) hydroactive 

 closing of the stomata would be reflected first at the base where regularly 

 higher water saturation deficits were observed. This closing would thus 

 act against the observed difference in the intensity of photosynthesis. 



Still greater, statistically significant differences were observed in the 

 respiration intensity. Average differences in the intensity of CO2 produc- 

 tion in the dark amounted to 0-31 ±007 jj-g COa/mg dry weight and 

 were statistically very significant (P=^oooooi). The average intensity of 

 respiration of the discs cut out from the apical part of the leaf-blade was 

 in the same experiment 2-38 j^tg/mg dry weight, while of those firom the 

 base it was on the average 1 3 per cent higher (number of sample pairs 

 «=82) (see Table i). In the course of estimation in the Warburg 

 apparatus the discs acquired within 90 min an average of 5-8 per cent 

 water saturation deficit. There were no significant differences between the 

 water deficit of the discs from the apical and basal part of the leaf-blade. 



In common with the intensity of photosynthesis the respiration intensity 

 of assimilatory tissues of the leaf-blade was signfficantly higher in the basal 

 part than in the apical one. 



DISCUSSION AND CONCLUSIONS 



Intensity of photosynthesis referred to leaf area was about 22% higher at 

 the base of tobacco leaf-blades than at their apical part. This statistically 

 very significant difference could be associated by about 1/9 only with the 

 greater area of stomatal pores at the leaf base where the density of stomata 

 is significantly higher but their area significantly smaller, so that the calcu- 

 lated relative index is 2-5 per cent greater at the base than at the apex. 

 Different opening width of the stomata affect the results only by decreasing 

 the observed difference (see Residts). The stomata played no role whatever 

 in the measurement of respiration, when they were photoactively closed. 

 Respiration intensity referred to dry weight was 1 3 per cent higher at the 

 base than in the apical part of the leaf-blade. This difference is also statisti- 

 cally very signfficant. It may be concluded that the observed statistically 

 very significant differences between the rate of photosynthesis and respira- 

 16 



