16 
BULLETIN" 993, U. S. DEPARTMENT OF AGRICULTURE. 
Figure 4 shows the periodical differences in acid content. Ap- 
parently the acid content of lemons varies more from month to month 
than any other constituent, the graphs being very irregular. It would 
seem that the Eureka variety has a rather well-defined period of low 
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Fig. 3. — Monthly averages of pounds of oil per ton of fruit. 
acidity in the late winter and spring months. Rising rapidly from 
that time, the acid is at its maximum in September, after which it 
again declines. The acidity of the Lisbon samples was much less 
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Fig. 4. — Monthly averages of pounds of acid per ton of fruit. 
uniform, the general trend of the curve being broken by several in- 
explicable irregularities. While the maximum occurs in September, 
as with the Eurekas, there is no well-defined minimum, low averages 
being shown in both July and October. During the first six months 
