346 



B. ORCHARD 



changes in either ratio. The differences between experiments in the 

 changes in dry matter distribution with time was probably caused by 

 differences in the weather. Radiation and temperature were particularly 

 unfavourable for growth during the final sampling interval in Exp. 3. 



Leaf Area (Fig. 4) 



The changes with time in leaf area index (L) were similar in all experiments ; 

 L reached a maximum when the plants were 3-4 months old and then 

 decreased. Maximum L was shghtly less in 1959 (5-3) than in 1958 (6-3) and 



15 



O 



O 5 



Expt I. 1958 



T t 



B Watered 

 TC. Started 



Expt 2. 1959 



I Sept 



Expt 3. I960 



July I Aug I Sept I July 1 Ajg I Sept Oct I Nov I Dec I 



Fig. 3. Lamina/petiole dry weight ratio. Symbols as Fig. i. 



much less in i960 (1-3). Area per leaf was similar in Exps. i and 2, so the 

 smaller maximum L was caused by a lower leaf number. In Exp. 3 low 

 temperature and radiation decreased both leaf expansion and, less severely, 

 leaf production. In all experiments the fall from the maximum was the 

 result of decrease in area per leaf, and leaf number continued to increase 

 with time (fig. 6). 



Maximum L was less than that reported by Owen (1958) (78) for beet 

 growing on the same plots but greater than that of sugar beet grown in 

 the field atRothamsted in 1958 (Orchard and Monteith, unpubUshed) or in 

 previous years (Watson, 1947). Maximum L was attained sUghtly earher 

 under glass than in the open. 



All drought treatments decreased L. The treatment B had the greatest 



