140 Butler.—A Study on Gummosis of Prunus and Citrus, with 
successfully employed in cases where trees are only subjected at one season 
of the year, or irregularly and accidentally, to conditions favourable to the 
development of gummosis. The bark of the affected trees may be slit} 
cross-wise, longitudinally, or spirally. For cases of generalized gummosis 
this latter method is the only efficient one. 
It is a common practice in the treatment of gummosis, and one that 
has been advocated in the literature, to cut the bark away on each side of the 
exudate until clean healthy tissues are reached, removing at the same time 
all infiltrated and discoloured wood. The wounds thus formed, and they 
frequently grow to an immense size, are then covered with wax, iron 
sulphate solution, a mixture of tar and phenol, Saint-Fiacre ungent, and 
a variety of other substances. This practice has, however, like most 
empirical remedies, more objectionable than unobjectionable features. The 
removal of the discoloured infiltrated wood is absolutely without justification, 
no matter how severely the trees may be affected by gummosis, and cutting 
away the bark is only advantageous after it has been killed, for we know 
that as long as the cambium remains alive it is capable, upon the re- 
establishment of normal conditions, of laying down xylem again immediately 
over the susceptible tissues or the gum masses resulting from their de- 
generation. The removal of the cambial layer while it is still alive is, 
therefore,'a serious error. Dead bark, on the other hand, should be cut 
away as a matter of hygiene, and also that the healing tissues may grow 
more easily over the area covered by it. 
The tissues exposed by the removal of the dead bark may be covered 
with shellac, or any other suitable substance provided it contains neither 
free acid nor free alkali. 
SUMMARY. 
I. Gummosis of Prunus and gummosis of Citrus are indistinguishable 
maladies. They are identical in histological development ; they are identical 
in their causal relationships ; no species in either genus is entirely immune 
to the disease, though in both the malady predominates in one (Citrus) 
or several species (Prunus); in both genera we find species in which the 
malady is predominately one of the fruit (citron and Saucer Peach)—in 
a word, any manifestation of gummosis observed in one genus will be found 
in replica in the other. 
II. Gummosis is due to hydrolysis of the walls of the embryonic wood 
cells, which develop into a susceptible tissue. The dissolution of the cell- 
walls begins in the secondary lamella and almost coincidently in the primary 
membrane ; the dissolution of the third lamella proceeds centripetally, and 
with its final destruction the cell contents become a part of the gum mass. 
III. The cell contents are at no time actively concerned in gum 
