Observations on Squamosis and Exanthema of the Citrus . 145 
pathognomonic structural characters of the xylem arise. Squamosis, how- 
ever, must be further studied before its cause or causes can be definitely 
ascertained. We are only certain of one thing : the disease is a form 
of gummosis, and consequently growth and water are factors in its 
development. 
5. Preventive and Remedial Measures. 
Little is known regarding the remedial and preventive methods for 
squamosis. The only preventive measure that appears, at present, to offer 
any guarantee of success is growth regulation. This may be accomplished 
by cultural methods. As for remedies, there are at present none. Slitting 
the bark may be considered a palliative, nothing more. 
IV. EXANTHEMA . 1 
1. Historical. 
Exanthema is at present only known in the United States. In Florida 
it is found throughout the orange-growing region, and has probably been 
a malady of the Citrus in that State since the introduction of their culture. 
In California exanthema is only known in the orange groves of Los Angeles, 
San Bernardino, and San Diego Counties, Southern California, and, as in 
the case of Florida, the date of the first appearance of the malady does not 
appear to have been recorded. 
2. Description. 
General. According to Hume, exanthema affects all varieties of the 
Citrus. Young trees— the malady has even been observed in nursery stock 
— and old trees are equally susceptible. The malady develops in California 
either on very permeable granitic soils or in shallow clay soils underlaid by 
an impermeable subsoil, in other words, in dry soils. In Florida the soils 
are typically sandy and belong, therefore, to the class of permeable dry 
soils. In that state the disease is worst when the soils are poorly drained 
or underlaid by an impermeable ferruginous sandstone, but it is also found 
in groves growing on the best ( hammock ’ soils. 
Minute . 2 Exanthema is characteristically a disease of the small 
branches and shoots, though the fruit shows symptoms of diagnostic value. 
1 Bibliography. 
Swingle, W. T., and Webber, H. J. : The Principal Diseases of Citrus Fruits in Florida. U.S. 
Dept. Agr., Div. Veg. Phys. and Path., Bull, viii, 1896, pp. 14-20. 
THOMAS, J. J. : The American Fruit Culturist, 1906, pp. 638-9. 
Hume, H. H. : Citrus Fruits and their Culture, 1904, pp. 488-92. 
: Some Citrus Troubles. Florida Agr. Expt. Sta., Bull, liii, T900, pp. 157-61. 
Smith, R. E., and Butler, O. : Gum Disease of Citrus Trees in California. Cal. Agr. Expt. Sta., 
Bull, cc, 1908, pp. 266-9. 
2 Largely after Swingle and Webber, loc. cit., p. 16 et seq. 
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