WATER SATURATION DEFICIT 103 



(i960) and others. These authors call the attention to the high WSD of 

 young leaves (as determined by Stocker's method) on plants under natural 

 conditions. Rutter and Sands (1958) and Sands andRutter (1958) bring out 

 the close relationship between the WSD and transpiration and soil humidity. 

 Both of their papers contain valuable data on the WSD values during 

 different water content of the soil. 



MATERIAL AND METHODS 



About ioo-150-day-old plants of fodder cabbage [Brassica oleracea L., 

 convar. acephala /DC. I Ahf., var. meduUosa Thell. in Hegi) of the sort 

 Markstammkohl, and of rape [Brassica napiis L., var. oleifera DC.) of the sort 

 Slapska, grown in pots in a greenhouse were used for the experiments. 

 Plants of both species had between 6 and 9 leaves. 



The water deficit was estimated by a method suggested earher (Catsky, 

 i960) modified for young leaves: a cork-borer was used to cut out discs of 

 8 mm in diameter from the leaves; the discs were then weighed, saturated 

 in openings (75 mm in diameter) in a moist plate of polyurethane foam. 

 After 3 hours of saturation the discs were taken out, dried with filter paper, 

 weighed and saturated again. After another 3 hours they were again dried, 

 weighed and desiccated at I05°C. The WSD was calculated by the 

 following formula: 



0/ ^3j) ^ {2x weight after 3 h)- (weight after 6 h)- initial wt. ^ ^^^ 

 [ix weight after 3 h) — (weight after 6 h) — dry wt. 



The apphcabiUty of this modification was confirmed by experiments to be 

 described in the experimental section. 



Other details of method will be presented with the individual 

 experiments. 



RESULTS 



I . Saturation Curve of Whole Leaves 



The experiments carried out in this section were to investigate the course of 

 water uptake by detached whole leaves during estimation of WSD 

 according to Stocker ; the results were to serve as a basis for the experiments 

 to be described later concerning the experimental proof of 'growth- 

 WSD'. Six young and 6 old leaves were detached from well-watered 

 plants in pots. The leaves were weighed and saturated in the dark through 

 8 



