| The Philippine Journal of Science 1921 
thickness and the greater toughness of the leaves differ in no way 
from the symptoms known in California as mottled leaf. 
According to this brief review, a number of causes have 
been ascribed to mottled leaf, all of them being advanced after 
a careful study of the disease which sometimes extended over a 
considerable period of time. It would seem reasonable to con- 
clude from this review of past studies that the complex of symp- 
toms known as mottled leaf may be induced by several different 
types of injury, any one of which may cause the same reaction of 
the plant. That is, several types of injury to citrus trees may 
produce the same ultimate reaction and symptoms. 
OBSERVATIONS ON MOTTLED LEAF AT LAMAO, PHILIPPINE ISLANDS 
_The Philippine Bureau of Agriculture maintains a horticul- 
tural station and plant propagation garden at Lamao, in Bataan 
Province near Manila. At this experiment station there are 
three orchards which contain a number of American and Jap- 
anese citrus varieties, and very extensive nurseries for the 
propagation of these varieties. These extensive collections and 
introductions are the work of Mr. P. J. Wester, of the Philippine 
Bureau of Agriculture. The writer is greatly indebted to Mr. 
Wester for assistance in identifying varieties at Lamao, and 
for numerous kindnesses in many other ways, and herein he ex- 
presses his deep appreciation to him. 
The orchard trees and nursery trees at Lamao are planted 
upon stocks of different species; the stocks represented are the 
pummelo (Citrus maxima), the cabuyao (Citrus hystrix), the 
sour orange (Citrus aurantium), the sweet orange (Citrus sin- 
ensis), the calamondin (Citrus mitis), and the mandarin orange 
(Citrus nobilis) . 
It was noticed that a considerable amount of mottled leaf was 
present in the nurseries, and that there was also mottled leaf in 
the mature orchards, although to a less extent. The type of 
mottling was entirely the same as that seen in California, the 
leaves yellowing slightly between the veins in the less-affected 
cases, while in the more severe cases the leaves became yellow 
to include all of the leaf-blade tissue with the exception of the 
main veins and midrib, which remained green. The affected 
leaves were stunted in size, thickened, and more leathery than 
were the normal leaves. It gradually became evident that there 
was a correlation between the occurrence of mottled leaf and the 
species used for a stock. A determination was made for each 
