232 BOHDAN SLAVIK 



tion of assimilatory tissues at the base and near the apex were not due to a 

 stomatal factor, i.e. neither to their different size and number nor to their 

 state. It should be noted here that in the experiments the effect of possible 

 differences in the permeabihty of the cuticle or of the whole epidermis for 

 CO 2 and the effect of the inner structure were not eUminated. In experi- 

 ments on photosynthesis the effect of possibly different chlorophyll content 

 could also play a role. 



The osmotic pressure of the cell sap was i8 per cent lower in the basal 

 part than in the apical one and this difference was also statistically very 

 significant. 



If the differences observed are correlated with differences in hydration of 

 the tissue expressed by diffemt osmotic pressure of the cell sap it is with the 

 awareness of the possibihty of an actual effect of the state of hydration as 

 well as of its structural consequences formed during leaf ontogeny. In other 

 words, the stable differences in hydration of leaf tissue cells as known from 

 the differences in the osmotic pressure of the cell sap represent both an actual 

 and an ontogenetic factor which has affected both the anatomical and 

 plasmatic structure of leaf tissue cells. These structures influence then the 

 intensity of functions, in our case of CO2 assimilation and respiration. 



A distinction between the actual effect of hydration and the ontogenetic 

 effect on structure and thus on function is difficult to make especially, if the 

 question of reversibiUty of these changes is considered. Many changes in 

 the photosynthetic activity due to dehydration are completely reversible 

 but not all of them (Stocker and Holdheide, 1937; Kaltwasser, 1939; 

 BrilUant, i949;PJed, 1953; Stocker, 1954; Ensgraber, 1954; Stalfelt, i960 

 and others). The additive irreversible changes become structurally per- 

 manent. Therefore, even those structural changes, the effect of which 

 could not be ehminated during the experiments described here and which 

 could not be distinguished from the actual effect of hydration are in fact 

 the consequences of dehydration. They can thus be causally connected with 

 hydration, particularly in such cases where the observed differences in 

 hydration at different parts of the leaf-blade are permanent as is the case in 

 our experiments. 



The observed relative differences in osmotic pressure of the cell sap are 

 practically independent of the tissue diffusion pressure deficit (Slavik 

 1959a). They persist even during complete water saturation, during 

 complete turgescence. The same relative differences may thus be ascribed 

 to the maximum cell turgor. These relative differences in the turgor pressure 

 are undoubtedly connected with relatively permanent structural differences. 



To my mind, the observed differences in the intensity of photosynthesis 



