DISEASES XOT DUE TO PARASITES AXD OF UXKXOWX ORIGIX 



1705 



chemical ccmposition of the soil. The conclusions are based upon a field 

 and laboratory study of 130 orange groves and 45 lemon groves mainlj- 

 situated in Riverside and San Bernardino Counties, CaUfornia. The per- 

 centage of mottled leaves was determined by examining 10 to 12 t3^pical 

 trees in each grove. A soil sample 3 feet in depth was taken near each tree, 

 each foot sample being kept separateh\ These samples were anah'sed, 

 for humus, organic carbon, mineral carbonates, bicarbonates and total 

 nitrogen. The most striking results are shown in Tables I and II. 



The moisture equivalent is a measure of the moisture retentiveness 

 of a soil, and is numerically equal to the percentage of moisture which 

 a given soil is able to retain in opposition to a centrifugal force 1000 

 times that of gravity. The finer the soil particles the greater is the 

 m.oisture equivalent. 



The following facts can be gleaned from tables I and II : 



Table I. — Analysis of orange grove soils, grouped according 

 to percentage of mottled leaves, each group containing about 20 groves. 



Table II. — Analyses of lemon grove soils, grouped according 

 to percentage of mottled leaves, each group including 8 groves. 



