I July I Aug I S«pt I July I Aug jSepl Oct | Nov | Dec | 



Fig. 8. Moisture content, (i960 roots, treatments B, C, not shown.) Symbols as Fig. i. 



The action of small applications of water on moisture content was small 

 even on the 1959 B plots where it affected leaf growth rate considerably. 



The moisture content changes were almost certainly not correlated in a 

 simple manner with turgor changes. The different response of tops and 

 roots to treatment, and the small effect of hght watering, indicate a change 

 in composition of the dry matter of the plant rather than reversible loss of 

 water. 



DISCUSSION 



The most interesting effect of weather was on the large stimulation of 

 growth by watering after drought (after effect) which apparently required 

 high radiation for its expression. The relative leaf growth rate during the 

 recovery from drought was significantly greater than that of the A plots in 

 both 1958 and 1959, but the effect on net assimilation rate (E) was significant 

 only in 1959 (Table 3). The increase in E, however, was associated with a 

 decrease in L and was insufficient to increase the crop growth rate. The 

 absence of a significant effect on E in 1958 might be explained by the small 

 effect of drought on leaf area in that year. This does not, however, explain 

 the absence of the phenomenon from the experiment in 1957 of Owen 

 (1958). Owen's treatment B had almost the same effect on L as the 1959 

 treatment but it had no after effect on E. Owen's B plants had twice the leaf 

 area but received less radiation than the 1959 B plants. Although it is possible 



