Florida Agricultural Experiment Station


that recent investigations in California show that certain baf-
fling diseases of other trees, such as mottling of apricot, rosette
of pecan, and yellows or little-leaf of walnut are closely related
to mottle-leaf in citrus and may be brought on by the same en-
vironmental conditions that induce the development of the lat-
ter trouble.
 Under California conditions, it has been found that there is
 a deficiency of calcium (lime) in the foliage of mottle-leaf trees
 and that any practice that tends to increase the alkalinity of the
 soil decreases the availability of calcium and hence induces the
 development of mottle-leaf. It should be borne in mind, how-
 ever, that the California citrus soils, for the most part, are more
 or less alkaline and are of entirely different composition and
 formation than Florida citrus soils, which, except for the lands
 with marly subsoils, are generally more or less acid in character.
 It is therefore obvious that what may apply in California in this
 case may not hold in Florida.
 Preliminary investigations by the chemistry department of the
 Florida Experiment Station, on the common type of mottle-leaf
 on the light sandy soils of Florida, give somewhat different
 results from those obtained in California, indicating an excess
 of calcium and a deficiency of iron in the foliage of mottle-leaf
 trees. They indicate, however, that the occurrence of mottle-leaf
 in Florida is associated with an alkaline condition of the soil.
 The low content of organic matter and low mineral content of
 Florida soils bring about a condition which could, under the fre-
 quently occurring unfavorable soil moisture conditions, result
 in a lack of availability of some of the required elements, par-
 ticularly the more difficultly soluble iron. The seasonal varia-
 tions in the occurrence of mottle-leaf, the frequent injury due
 to applications of limestone in the lighter types of sandy soils,
 and the applications of excessive amounts of potash to Florida
 soils, combined with their low iron content, seem to indicate that
 mottle-leaf in Florida may, in part at least, be due to a lack of
 available iron.
 Considerable evidence was presented some years ago to show
 that the cause of the lime-induced chlorosis on soils with marly
 subsoils was due to the inability of the trees to get sufficient iron,
 an element quite essential to the formation of the green coloring
matter in the leaves. According to the explanation given by Lip-
man in 1921, the presence of an excess of lime as calcium car-