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(c) Thelycrania sangiiinea 



MARGARET S. JARVIS 



II relative to the control (moisture regime O) than was that of F. vulgaris. 

 For T. sanguinea there were significant differences in total leaf area per 

 plant between treatments O and I after 60 days ; and between treatments 

 O and I, and I and II after 84 days: for P. padns the differences between 

 treatments in total leaf area per plant were not significant after 92 days. 

 For each of these woody species, one of the most striking effects of increased 

 SMT was the abscission of some of the mature leaves, so that, during the 

 whole or part of the period of the experiment there was a net reduction in 

 leaf number for plants in treatments I and II but a net gain in treatment O. 

 The changes in total leaf area per plant throughout the experiment, there- 

 fore, represent the difference between the increase in leaf area resulting 

 from production and expansion of new leaves and the decrease resulting 

 from the abscission of mature leaves. There was no such loss of leaves from 

 plants of treatment O for either species. The production and expansion of 

 new leaves at the shoot apices of T. sanguinea was continuous throughout 

 the experimental period, provided that soil moisture tension was not 

 hmiting. However, in P. padus leaf production was not continuous but 

 occurred in flushes, as is common for many tree species. In a second 

 experiment, with first-year seedhngs of P. padus, there was no further 

 expansion or production of leaves during three months of the three 

 moisture regime treatments. In treatments I and II aU leaves abscissed ; in 

 treatment O all leaves remained apparently healthy. (In the following spring 

 the plants from the three treatments grew vigorously, in soil kept watered.) 



