WATER SATURATION DEFICIT 



105 



be produced) were then saturated in the polyurethane plate. It follows 

 from the results that the experimental discs reached the control curve, i.e. 

 that growth persisted in spite of interrupted water supply and gave rise to 

 a growth WSD (Fig. 2). 



Fig. 2. Saturation of two sets of discs from young leaves in one of which water supply 

 was cut oif between the third and fourth hour. For details see the text. 



3. Verification of the Applicability of the Method of WSD 

 Estimation by Means of Extrapolation 



It was the aim of the following experiments to test the apphcability of 

 extrapolation (Yemm and WiUis, 1954) in estimating the WSD by the 

 'disc method'. Experimental leaves were saturated in the dark for 24 hours 

 with their petioles immersed in water in a water-saturated atmosphere. 

 After that, rectangles of leaf tissue without large nerves were cut out from 

 them, well dried and left to wilt on a nylon mesh. After reaching a certain 

 WSD, which was calculated from the observed loss in weight of the initially 

 saturated rectangles, discs were cut out from the whole area of the sample 

 and their WSD estimated after saturation in a polyurethane plate by extra- 



