GROWTH RESPONSE OF SUGAR BEET 



345 



mainly because dry matter was suddenly lost from the tops possibly as a 

 response to the i in. of water appHed during the last sampling period, and 

 not because of a steadily mounting drought effect. The treatments had no 

 significant effect in Exp. 3 ; the large differences were the result of initial 

 variation between plots. The relative growth rate was not affected except 

 during the last interval when it was decreased by treatment B. 



The dry matter contents of the various parts of the plant were not equally 

 affected by drought. In Expts. i and 2 the top/root dry weight ratio (Fig. 2) 



Expt I. 1958 



ExDt 2 1959 



Expt 3 I960 



3 - 



IT 



B. Watered 



T 



C. Started 



July I Aug I Sept 



Jul 



Aug I Sept Oct 



Nov 



I Dec I 



Fig. 2. Top/root dry weight ratio. Symbols as Fig. i. 



and the lamina/petiole dry weight ratio (Fig. 3) fell uniformly with time. 

 The effect of drought was small and acted oppositely on the two ratios. 

 The decreased yields were entirely in the tops ; the weight of roots was 

 unaffected, so the decrease with time in top/root ratio was accentuated. In 

 contrast, the time trend in lamina/petiole ratio was decreased by drought, 

 the yield of lamina being decreased less than the yield of petioles. The 

 results of the two experiments were consistent but in 1958 the drought 

 effects were not significant. In 1959, whereas the effect of the C treatment 

 was only just significant, treatment B had a highly significant effect on the 

 top/root ratio, and increased the lamina/petiole ratio significantly during 

 the recovery phase. 



In Exp. 3 the top/root ratio fell at first and then became almost constant, 

 the lamina/petiole ratio fell a httle and then rose slightly. The lower growth 

 rate of the BL plots during the fmal interval was not accompanied by 



