May 7,1917 Citrus Leaves at Various Stages of Mottling 159 
mulched basin, when the decomposition products come into direct 
contact with the rootlets of the tree. 
The mineral composition of Citrus leaves is subject to much variation, 
and the' age of the leaf is an important factor to bear in mind when 
selecting leaves for comparative study. Since Citrus trees retain their 
leaves for two to three years, it is often difficult to determine the age of 
a certain leaf. Especially is this true of a leaf in the last stages of 
mottling, which, even when but 2 or 3, months old, often looks to be 2 
or 3 years old. 
It is also not a safe procedure to compare mottled leaves from a grove 
in a badly mottled condition with healthy leaves from another grove in a 
good condition, especially if the two groves are on different soil types. 
In describing the mottled conditions of the leaves here discussed, the 
terms “first stage,” “secondstage,” and soon to the “fifth stage” were used. 
These terms mean that stage 1 represents the first definite appearance 
of mottling, the mottled or chlorotic spots being limited to one to 
three small spots on each side of the midrib, the spots in this stage being 
usually confined to the upper part of the leaf. The fifth, or last, stage is 
the other extreme, which represents a leaf where only the midrib may 
retain a little chlorophyll or none at all. The stages 2, 3, and 4 simply 
represent conditions of increasing mottling and range between stages 
1 and 5. The various stages are represented in color in one of the publi¬ 
cations already cited (2). 
In Table I are given the percentages of iron, calcium, magnesium, and 
phosphoric acid found in orange and lemon leaves in various stages of 
mottling, and also the relative distribution of these elements. The 
leaves were all of new spring growth and were collected on the fertilizer 
experiment plots of the University of California Citrus Experiment Sta¬ 
tion, Riverside. In each table the healthy leaves—that is, those with 
only a trace of mottling—are from trees on the manure plots, and the 
mottled leaves are from trees on the sodium-nitrate plots. These plots 
are side by side and represent very extreme tree conditions not only so 
far as leaf mottling is concerned but also as regards foliage density, 
fruiting, etc. 
Considering the average composition of the entire leaves, the per¬ 
centages of calcium, magnesium, and phosphoric acid increase as the 
mottling increases, in both the orange and lemon leaves. There is but 
one exception, that of the phosphoric acid in the last stage of mottling 
in the lemon leaves. 
In most cases the ratio of the percentages of the determined elements 
in the leaves to those in the midribs diminishes slightly as mottling in¬ 
creases, though this variation is not very marked. 
In each kind of leaves the average percentage of iron is highest in the 
healthy leaves and is least in stages 3 and 4. 
