V / V 



I04 



JIRICATSKY 



their petiole immersed in water in a water-saturated atmosphere. At given 

 time intervals the leaves were dried with a filter paper and weighed. Water 

 uptake was expressed as percent initial value after subtracting the dry- 

 weight. The result (Fig. i) clearly demonstrates the qualitative difference 

 between the saturation curves of young and of old leaves. 



Fig. I . Saturation of old (1,2) and young (3 , 4) leaves in estimating the water saturation 

 deficit by Stocker's method, i, 3-rape; 2, 4-fodder cabbage. Abscissa: time of 

 saturation in hours ; ordinate : weight of water in per cent initial weight. 



2. Origin of *Growth-WSD' in Leaf Tissue Discs 



Experiments shown in Fig. 2 were designed to demonstrate experimentally 

 the origin of the 'growth-WSD' and its subsequent disappearance. Two 

 equal sets of discs were cut out from young leaves of fodder cabbage and 

 saturated in the polyurethane plate (see Methods). After 3 hours the discs 

 were weighed ; the control ones were saturated further and the experimental 

 ones were placed on a nylon mesh in a Petri dish containing a water-satu- 

 rated atmosphere and placed in darkness. After i hour, these experimental 

 discs (in which a growth WSD and hence an actual WSD was presumed to 



