May 7,1917 Citrus Leaves at Various Stages of Mottling 165 
than the mesophyll tissue, usually as much magnesium, and usually 
more phosphoric acid. 
With very few minor exceptions, the leaf stems contained less iron, 
calcium, and magnesium than either the midrib or mesophyll area in 
both healthy and mottled leaves. The percentages of calcium, magne¬ 
sium, and phosphoric acid,*however, increased in the leaf stems of badly 
mottled Citrus leaves, but usually not in the medium mottled leaves. 
Old leaves contained higher percentages of calcium and magnesium 
than new leaves not fully grown. 
In all the Citrus leaves analyzed, the phosphoric acid was quite uni¬ 
formly distributed in the midribs, the mesophyll tissue, and the leaf 
stems (regardless of age or stage of mottling), indicating that phos¬ 
phoric acid is early and freely transferred through the conducting tissue 
to the mespohyll areas. 
Sharply outlined yellow spots in the mesophyll areas of orange leaves 
contained less calcium, magnesium, and phosphoric acid than the green 
parts (mostly veins) of the leaves. 
Green leaves and the green parts of spotted leaves of the golden privet 
contained about twice as much calcium and appreciably more magnesium 
than the yellow leaves. Yellow leaves and the yellow parts of spotted 
leaves contained more iron than and about 2.5 times as much phosphoric 
acid as the green leaves or green parts of spotted leaves. 
Leaf stems of green privet leaves’contained lower percentages of iron, 
calcium, magnesium, and phosphoric acid than the leaves. 
Teaf stems of yellow privet leaves contained about one-half as much 
phosphoric acid as the leaves; the percentages of iron and magnesium 
were about the same, while the leaf stems contained more calcium than 
the leaves. The leaf stems of yellow privet leaves contained higher 
percentages of calcium and magnesium than the leaf stems of green 
privet leaves. 
Judged by a comparison of the average percentages of the inorganic 
elements determined in healthy Citrus leaves and in leaves in the medium 
stages of mottling, the data obtained did not show that the initial mot¬ 
tling could be accounted for by deficiency in the transfer of the iron, 
calcium, magnesium, and phosphoric acid from the conducting system 
of the leaf stem and midrib to the mesophyll tissue. 
On the-other hand, sharply localized yeliow areas in old orange leaves 
contained less of these elements than the adjoining green areas (mostly 
veins), but whether that relation obtained in the initial stage of mot¬ 
tling was not determined. 
In very badly mottled Citrus leaves there was in general an increase in 
the percentage of these elements in the conducting tissues, including the • 
leaf stems, indicating difficulty in their transfer to the mesophyll tissues 
in very advanced stages of mottling, probably because the leaf had become 
functionless. 
