242 



F. H. WHITEHEAD 



TIME TO "death" IN RELATION TO SOIL MOISTURE 



O Time to "Death" 

 • lnt«rnod« Length 

 O Lea t Area 



r300 £ 



•x 



< 



Ul 



200 P 



LU 



2 



Fig. 6. Leaf areas and internode lengths of plants grown at four soil moisture levels 

 and the time taken for 'death' of these plants to occur in a 40 mile/h wind. 



plant since loss from the leaves would tend to be reduced if they are 

 covered with a fdm of water. The vahdity of this hypothesis was demon- 

 strated by growing plants of Helianthus annuus in the wind tunnel, one set 

 of which were kept sprayed with distilled water. The results are shown in 

 Fig. 7 (Whitehead, 1962). It can be seen that the extent of modification in 

 the sprayed plants is less than that of the controls. 



EFFECT OF CONTINOUS WATER SPRAY-LEAF ARE A-INTERNODE LENGTH 



5 0l 



E 40 



< 



UJ 3 0- 



cC 

 < 



20 



10 



AREA WITHOUT SPRAY 



APEA WITH SPRAY 



GE INTERNODE LENGTH 



UT SPRAY 



GE INTERNODE 



SPRAY 



LENGTH 



To" 



WIND 



20 30 



SPEED (m.p.h.) 



X 



I- 



UJ 



_i 



4 UJ 

 a 

 O 



3i 



Ul 



H 



2? 



UJ 



I ^ 

 a. 



Ul 



> 



< 



Fig. 7. Leaf areas»and average internode lengths of plants grown, with and without a 

 continuous water spray, for 35 days at mid speeds of i, 9, 19 and 33 mile/h winds. 



