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DAYS AFTER TREATMENT 



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Fig. 7. Effect of treatment with gii)bereiiin on the starch content of rice phtnts. 



crease the light reception, and, therefore, increase carbon dioxide 

 fixation. 



Among these possibihties, the second seems to be most feasible in 

 view of the data given in Figures 2 and 3 and Table 2. The photosyn- 

 thetic activity per unit leaf area does not change as the result of the 

 GA treatment; but owing to the increase in leaf area, the photosyn- 

 thetic activity of the whole plant increases. 



In these experiments, sufficient fertilizer was supplied. If the fer- 

 tilizer supply is insufficient, the leaves may become yellowish by GA 

 treatment, the photosynthetic activity per leaf area should then de- 

 crease and the activity per whole plant may also decrease. 



In rice plants, the increase in the sheath area by GA treatment is 

 often larger than the increase in the leaf area as in the example given 

 in Figure 3. In this instance that may be important in increasing 

 carbon dioxide fixation. Brian et al. (1) and others have previously 

 referred to this possibility. 



An increase in the efficiency of light reception due to the change 

 in plant shape may also be working in these experiments. In plants 

 which are grown in groups, and sid)je( ted to mutual overlapping in 

 the field, an increase in the efficiency of light reception by GA treat- 

 ment may be appreciable. 



