Observations on Squamosis and Exanthema of the Citrus . 141 
formation. Starch, it should be emphasized, contrary to the prevalent 
view, plays no role whatsoever in gum formation. 
IV. The secondary lamella of the wood fibres and that of the vessels, 
as well as parenchymatous tissue, may show gummous degeneration in 
severe cases of gummosis when they are near the zone of active development 
of the malady. 
V. Gummosis develops autogenously and is induced by all manner 
of traumatisms, provided they act directly or indirectly as growth stimulants 
to the cambium. Once incited the simultaneous concurrence of two con- 
ditions, one physiological, the other environmental, is necessary for the 
development of the disease ; the cambium must be actively growing and 
an abundant supply of water must be available to the roots ; either factor 
is inoperative alone. 
III. SQUAMOSIS. 1 
Syn. : Scaly bark. 
1. Historical. 
Squamosis is at present only known in the Citrus groves of Southern 
California and Florida. The malady was probably first observed in 
California prior to 1880, but it has always remained so inactive that little 
or no attention has been paid to it. In Florida, on the other hand, squa- 
mosis has recently excited some interest, though its general behaviour in 
that State must be very much the same as in California, since it was first 
observed there about i860. 
1. Description. 
General Squamosis is primarily a disease of the orange-tree ; in fact, 
the malady does not appear to have been observed on the other Citrus. 
The disease always develops sporadically, and the conditions that favour its 
development appear only to occur at infrequent and long intervals of time. 
I have a note regarding an orange grove in which, during a period of twenty 
years, no new trees became affected. 
Besides the infrequency of its appearance in Citrus groves, squamosis 
has another marked peculiarity : the disease develops extremely slowly on 
the affected trees. The scaling of the bark, which is the striking and 
characteristic symptom of squamosis, first appears as a single scale or group 
of scales upon the trunk or limbs, the area of affected tissues gradually 
growing from this small beginning until the trunk or the limbs are com- 
pletely girdled. An affected tree may live for fifteen to twenty years, but 
1 Bibliography. 
Smith, R. E., and O. Butler : Gum Disease of Citrus Trees in California. California Agr. Expt. 
Sta., Bull, cc, 1908, pp. 256-63. 
Fawcett, H. S. : Report of Assistant Plant Pathologist. Florida Agr. Expt. Sta. Report, 1907. 
: Scaly Bark of Citrus, Florida Agr. Expt. Sta., Bull, xcviii, 1909, pp. 75-80, 
