60r 



GROWTH RESPONSE OF SUGAR BEET 349 



Expt. I 1958 Expt. 2 1959 Expt. 3 I960 



I July I Aug I Sept I July I Aug |Sept Oct | Nov | Dec | 



Fig. 7. Net assimilation rate. Symbols as Fig. i. 



Net Assimilation Rate (Fig. 7) 



The net assimilation rate (E) differed significantly between experiments, 

 and was greatest in 1959 and least in i960, in accordance with the observed 

 differences in total radiation. E was not depressed consistently by water 

 shortage. The 1959 drought did, however, have a significant after effect on 

 E; when the drought was broken by ^ in. of water, E was increased signifi- 

 cantly. This increase persisted for a second 14-day period during which 

 the plots were returned to field capacity. 



Moisture Content (Fig. 8) 



The moisture content fell with time, more slowly in Exp. 3 in which the 

 mean moisture content was slightly less than in Exps. i and 2. The moisture 

 content of the tops was greater than that of the roots and was affected more 

 by treatment. The drought effect (relative to the A value) was similar in all 

 three experiments ; drought decreased the moisture content of the plants 

 by 26-30% and restoring the plots to field capacity restored the moisture 

 content to within 10% of the A value before the next samphng occasion. 



