124 Butler—A Study on Gummosts of Prunus and Critus, with 
alcohol alone, must be used if the earlier stages of the disease were to be 
preserved. I early determined that when alcohol and glycerine, equal 
parts, was used as the fixing and preserving fluid, sections of shoots in 
which very young gum pockets were to be found always showed a great 
paucity of gum in the lacunae. I also observed that the glycerine-alcohol 
solution became more viscous when specimens had stood in it for sufficient 
time, and this viscosity, upon analysis, proved to be due to dissolved 
gum. Contrary to Mikosch’s observations, then, gum is ‘soluble in 50 % 
alcohol. As woody tissues are always hardened in alcohol, it became 
a matter of no small interest to determine what was the ininimum strength 
of alcohol in which the gum remained insoluble. I selected a sample 
of fresh fluid pellucid cherry gum—in other words, gum recently formed— 
and placed aliquot parts of it in 50%, 75%, 85% and 95 % alcohol. The 
gum dissolved in all but the 95 % solution. In alcohol of this strength the 
gum lost somewhat in volume, and became brittle and perfectly translucent, 
except at one corner where it was somewhat white opaque. 
In acetic acid the gum is quite soluble except in a large excess of the 
reagent. 
Farmer’s fixing solution (alcohol absolute 2 pts., glacial acetic acid 
1 pt.) may be used in lieu of 95 % alcohol, but the gum, instead of remaining 
a homogeneous mass, appears as a fine precipitate which is not very suitable 
for study. 
Mikosch found in the course of his study on gummosis of the cherry 
that staining reagents were of little or no avail, chloriodide of zinc being in 
all cases the most trustworthy. This opinion is, however, only relatively 
true. The gum behaves differently towards stains when young than when 
old, and at its incipiency its reactions cannot be made out at all, for the 
simple reason that it is too soluble in water ; the gum passes into solution 
and is lost. For this stage a differential alcoholic stain would be necessary, 
and up to the present I have found none. If we cut our sections, on the 
other hand, from material showing well-formed gum pockets, and in which, 
even in alcoholic solution, the gum occupies the lacunae as a homogeneous 
mass, the gum will be found to stain with Bohmer’s haematoxylin? usually 
more rapidly than the cellulose walls (Citrus in particular) or colour yellow 
in chloriodide of zinc (Prunus and Citrus). If now sections are taken 
through diseased material in which the gum pockets are well developed, 
and the gum in the lacunae has assumed centrally a yellow tinge, it will 
be found that Bohmer’s haematoxylin stains the gum peripherally (i.e. 
where colourless), but has little or no effect where it alteady shows coloration. 
Chloriodide of zinc in these cases gives no valuable indications at all; it is 
1 For formula vide Zimmermann, A.: Micro-technique, p. 181. Delafield’s haematoxylin 
(cf. Chamberlain, C. J. : Methods in Plant Histolo; » 249) isa i i 
pc angsien lawn kde: ZY, P- 249) more energetic stain, but does not 
