JOINAL OF MCffllM, BESEAM 
Vol. IX Washington, D. C., May 7, 1917 No. 6 
COMPOSITION OF CITRUS LEAVES AT VARIOUS 
STAGES OF MOTTLING 
By Charles A Jensen, 
Assistant in Plant Malnutrition, Office of Biophysical Investigations, Bureau of Plant 
Industry, United States Department of Agriculture 
A study of the soil factors influencing the mottling of Citrus leaves in 
southern California showed that the percentage of humus in the soils of 
the Citrus groves varied inversely with the mottling of the leaves, and 
this inverse relation showed a correlation of 67 per cent (2). 1 In another 
study it was found that organic matter, whether derived from stable 
manures, artificially produced manures from various green cover-crop 
materials, or by acid hydrolysis of sugar and hay material, attacked the 
soil minerals and liberated iron, calcium, magnesium, and phosphoric 
acid. 2 In another study on the mulched-basin system (3) it was found 
that on certain soil types this system caused a considerable diminution 
of leaf-mottling on orange trees (Citrus aurantium ). 
In view of these three facts it seemed possible that the mottling of 
Citrus leaves in southern California might possibly be due in part to a 
lack of supply of the mineral nutrients supposed to be most closely con¬ 
nected with the formation of chlorophyll. For this reason, Citrus leaves 
in various stages of mottling were collected and the iron, magnesium, 
calcium, and phosphoric-acid contents determined. The leaves in the 
various stages of mottling were collected from trees in the same grove, 
and in some cases from the same trees, so as to eliminate, as far as pos¬ 
sible, the influence of variations in soil type. 
Willstatter (11) has established the fact that the chlorophyll of all 
classes of plants contains magnesium and no other metal, and that the 
magnesium in the chlorophyll has an important part in the assimilation 
of carbon dioxid. Mameli (5,6), in growing a number of plants in media 
lacking in magnesium, found that the plants were etiolated or pale green 
and the chloroplasts abnormal in form as well as in color. She further 
states that comparative analysis showed a smaller percentage of mag¬ 
nesium in chlorotic or discolored leaves or leaf parts than in normal por¬ 
tions of the same plant. 
1 Reference is made by number to “Literature cited,” p. 166. 
2 Jensen, Charles A. Effect of decomposing organic matter on the solubility of certain inorganic con¬ 
stituents of the soil, particularly in its bearing on mottle-leaf of Citrus trees. Not yet published . 
Journal of Agricultural Research, 
Washington, D. C. 
if 
(157) 
Vol. IX, No. 6 
May 7,1917 
Key No. G 109 
