3o6 MARGARET S.JARVIS 



Table 4 



The mean leaf water deficits (LWD) developed by leaves on detached shoots ofPrunus 

 padiis and Thelycrania sanguinea after droughting. Same experiments as Table 3. LWDs 

 for leaves which did not regain turgor when left overnight in a saturated atmosphere 

 with their petioles in water, after the droughting treatment, were calculated by using 

 a value for the saturated weight obtained from the ratio of mean saturated weight to 

 dry weight for those leaves, in the same experiment, which recovered. The value for 

 critical LWD (the largest LWD from which turgidity can be regained) is between the 

 largest LWD from which recovery occurred and the smallest from which recovery 



did not occur 



slightly lower for T. sanguinea than for P. padus. This conclusion is based 

 on the results of the experiment where shoots of the species were droughted. 

 together. All the leaves of T. sanguinea, compared with 66% of leaves of 

 P. padns, recovered from the effect of 78%RH; and 40% of the leaves of 

 T. sanguinea recovered from the effect of 67%RH, while no P. padns leaves 

 did so. However, this difference is of the same magnitude as that obtaining 

 between leaves of the same species collected from different locaHties, or of 

 different ages, e.g., only 30% of leaves of P. padns collected from a Norfolk 

 fen (experiment of 14.9.59) recovered from the effect of 78% RH, com- 

 pared with 100% of leaves collected in Sheffield (experiment of 10.5.60) 

 and 66% for the same tree, two months later (experiment of 14.7.60). 



