118 Butler—A Study on Gummosts of Prunus and Citrus, with 
the Lago di Garda! In Sicily the disease was first observed in the pro- 
vince of Messina in 1862,2 and was also discovered about this time or some- 
what later in Spain, Corsica, and Algeria. The groves of New South Wales 
were devastated between 1860 and 1870.3 According to Curtis * the disease 
probably appeared about 1876 in Florida, though few people, he remarked, 
could remember seeing it prior to 1880; in California it was observed in 
1875.6 At the present day gummosis is known wherever the Citrus are 
extensively grown. 
2. DESCRIPTION. 
General. Unlike most maladies gummosis appears to be autogenous 
as well as superinduced by traumatisms of very diverse nature. Fungous, 
insectile, physical and chemical injuries, when they affect directly the 
cambium layer, all induce gummosis, provided growth is taking place. 
Furthermore, gum is not produced in quantities unless the tree affected is 
well supplied with water. The development of the disease depends, then, 
upon the rapidity with which new tissues are being laid down at the time of 
its initiation; and this rapidity, as is well known, is a function, broadly 
speaking, of the amount of water available to the roots of the affected tree. 
Growth and water are, therefore, essential to the appearance of gummosis, 
and both are limiting factors. The relation of these two factors, growth 
and waver, to gum formation, here only postulated, will be more fully dealt 
with in subsequent pages of this memoir, and is mentioned at this time 
solely with the view of rendering more comprehensible the development of 
gummosis in the orchard, and the cultural and environmental conditions 
affecting the same. 
Gummosis develops sporadically, sub-generally, or generally, depending 
on the nature of the inducing factor. It is usually only sporadic in the 
case of insect attack, and the same remark is true for many of the fungi. 
Some fungus-parasites, notably Coryneum Beyerinckit and Clasterosporium 
carpophilum, produce, on the other hand, sub-general or general gummosis, 
the atmospheric conditions favourable to the development of these parasites 
being also favourable to the formation of gumogenetic tissues in the host, 
Autogenous gummosis appears sporadically or sub-generally. In most 
species of Prunus and Citrus, the disease develops sporadically, only 
becoming generalized, as a rule, in P. Cerasus, P. avium, and Citrus 
Limonum. 
? Rapporto della Commissione 
Agricoltura Siciliana, n.s., i. 
2 Ibid. 
° Alderton, G. E.: Treatise and Handbook of Oran, 
* Curtis, A. H.: Sore Shin or Gum Disease. 
* Mills, J. W.: Citrus Fruit Culture, 
per studiare la malattia degli agrumi in Sicilia, &c. Annali di 
ge Culture in Auckland, New Zealand. 
Florida Agr. Expt. Sta., Bull. ii, 
California Agr. Experiment Sta., Bull. exxxvi., 
