18,1 Lee: Mottled Leaf of Citrus Trees 87 
and that the soil fiora of that locality possibly was not able to 
convert the nitrogen into an available form. 
Briggs, Jensen, and McLane,® in 1916, found that mottled 
leaf in citrus was correlated in a large number of cases with 
a low humus content. 
McBeth® showed, in 1917, that mottled leaves generally have a 
higher nitrogen content and a higher moisture content than nor- 
mal leaves. He concluded from his work that an irregular food 
and moisture supply was a cause of mottled leaf, and corroborated 
the view advanced by Smith and Smith. Briggs, Jensen, and 
McLane,”® in 1917, showed control of mottled leaf in a number of 
cases by the use of mulches, combined with basin irrigation, 
which carried organic material into the soil and also maintained 
the temperature of the soil more uniformly. They concluded 
that lack of humus is a cause of mottled leaf. The use of the 
mulched basin system of irrigation has not been accepted gen- 
erally by growers, however, because this practice possesses 
several disadvantages. 
Jensen," in 1917, showed that very badly mottled leaves of 
orange and lemon contained higher percentages of iron, calcium, 
magnesium, and phosphoric acid than did healthy leaves. He 
also observed, in general, an increase in the percentage of these 
elements in the leaf stems and midribs, indicating difficulty in 
their transfer to the mesophyll tissues in the later stages of 
mottling. This apparently is not advanced as a cause but as a 
contribution to the general understanding of the disease. 
Floyd,” in 1917, found mottled leaf in Florida to be correlated 
with the use of excessive amounts of ground limestone. He was 
able to induce the mottled leaf symptoms by adding ground lime- 
stone to the soil of potted plants. The writer has seen the 
mottled leaf in Florida which Floyd describes; apparently the 
yellowing between the veins, the stunting of the leaves, and the 
* Briggs, L. J., Jensen, C. A., and McLane, J. W., Mottle-leaf of citrus 
trees in relation to soil conditions, Journ. Agr. Res. 6 (1916) 721-759. 
* McBeth, I. G., Relation of the transformation and distribution of soil 
nitrogen to the nutrition of citrus plants, in Journ. Agr. Res. 9 (1917) 
183. : 
” Briggs, L. J., Jensen, C. A., and McLane, J. W., The mulched basin 
system of irrigated citrus culture and its bearing on the control of mottle- 
leaf, U. S. Dept. Agr. Bull. 499, professional paper (1917). 
4 Jensen, C. A., Citrus leaves at various stages of mottling. In Journ. 
Agr. Res. 9 (1917). 
“ Floyd, B. F., Some cases of injury to citrus trees apparently induced 
by ground limestone, Florida Agr. Exp. Sta. Bull. 137 (1917). 
