44 CALIFORNIA CITRUS CULTURE. 
cultivation, usually consequent upon the cementing lime carbonate in 
the water used in irrig:tion. Cultivating at different depths will tend 
to break this up and relieve the trees. Dynamite will break up the 
deep or natural hardpan. The trio of remedies for physiological ills 
is right irrigation, cultivation and fertilization. 
Exanthema—Florida Die-Back. 
(Fic. 22.) 
This disease is not well understood. The ends of the branches die; 
frequently tufts of small twigs develop from supernumerary buds; the 
bark roughens and shows lines of brown excrescence; gum pockets form 
near the attachment of the leaves; the fruit is imperfect and often pale 
yellow and insipid, and gum ferms in the fruit close akout the core; 
dark green leaves appear, which, though they would seem to indicate 
health, are really the result of the disease. It is claimed that gravelly 
soils with coarse gravel for subsoils, or soils underlaid with hardpan 
promote this disease, as do large appheations of stable fertilizer on such 
soils, especially if the trees have previously lacked plant food. As 
above advised, good care and removing the cause when possible is the 
only known cure. 
Gummosis—Gum Disease. 
Mr. H. 8. Fawcett has shown that gum disease is often fungoid. The 
gum is an incident. Fungoid attack of the bark is the real disease. It 
affects all kinds of citrus trees, but lemons suffer most. Gum exudes at 
various places, but in case of lemons, most at the crown near or at the 
place where the bud was inserted. Injuries, improper irrigation and 
earth compacted about the spot where the bud was inserted are enough 
to cause the disease. It is best to have the bud above the earth and 
avoid running water about the crown. 
Mr. Faweett has produced gum disease of the lemon by inoculations 
with the decaying bark; also from cultures. He finds two distinct 
forms, both produced by common molds of the packing-house. In one, 
the brown rot fungus (Pythiacystis citrophthora), the decay of the 
inner and outer bark is almost coincident, and the diseased bark remains 
hard, while in the other, gray fungus (Botrytis vulgaris), the outer 
hark decays before the inner, and all becomes soft. The eure for both 
is Bordeaux paste. (See Monthly Bulletin, Vol. 2, No. 8, page 601, 
August, 1913.) 
Psorosus—Scaly Bark. 
(Fic. 23.) 
This trouble, not found in the lemon, is described in its name. The 
cause ay be improper aeration or irrigation. When serious it is often 
