226 BOHDAN SLAVIK 



than at complete water saturation. Stocker(i954, 1956), who was concerned 

 with higher plants, entertained no doubt about the intensity of photo- 

 synthesis being dependent directly on the chemical potential of water in 

 the assimilating tissue. A similar view is held by Alexeev and his school 

 (1952, 1954) who found very significant correlations between the intensity 

 of photosynthesis and various indicators of the water relations of the 

 tissue, particularly between the colloid-bound water and the osmotic 

 pressure of the cell sap. 



The papers mentioned represent but a few examples of the fundamental 

 viewpoints extant rather than an exhaustive review of all papers where the 

 problem in question is touched upon. Such review of papers prior to the 

 early forties may be found in the monograph by Brilliant (1949), another is 

 given by Stalfelt (i960). 



The present communication should contribute to the problem from an 

 entirely nev/ and different point of view. 



In keeping with the physiological gradients in plant organs (Prat, 1948, 

 195 1) it was shown earlier (Slavik, 1959a, 1959b) that sugar-beet and tobacco 

 possessed a definite distribution pattern of values of the osmotic pressure of 

 the cell sap over the leaf-blade which did not change even during a com- 

 plete saturation of the leaf-blade with water, i.e. at a zero diffusion pressure 

 deficit of tissues in situ, and which was thus associated with an identical 

 gradient of the turgor pressure. This osmotic pressure gradient remained 

 relatively unchanged both during active (supplementary saturation) and 

 passive (wilting) water balance. I am of the opinion that such a natural and 

 constant difference in the cell sap osmotic pressure under normal conditions 

 in a steady state of individually identical material (one and the same leaf- 

 blade) is very suitable for studying the relationship between hydration and 

 the photosynthetic or respiratory activity. 



The present paper thus attempts to compare the differences in the 

 intensity of photosynthesis and respiration at the base and at the apex of 

 the leaf-blade, i.e. in those leaf-blade sections between which the greatest 

 natural and permanent differences in the osmotic pressure of the cell sap 

 are known to exist (for details see Slavik, 1959a). 



MATERIAL AND METHODS 



About 120-150-day-old tobacco plants [Nicotiana Sanderae hort.) in the 

 vegetative state with a leaf rosette of 10 to 12 leaves, grown in pots, were 

 used for the experiments. 



For the purpose of measuring the intensity of photosynthesis the plants 



