114 Butler—A Study on Gummosis of Prunus and Citrus, with 
in December gummed slowly and less abundantly, and, finally, branches 
removed in May, when the trees were in leaf, did not show any symptoms 
of gummosis. There thus appeared to be a certain relation between the 
time of year at which the branches were cut and their gumogenetic power. 
Mikosch observed and mentioned this apparent correlation, but offered no 
explanation for it. 
Cherry gum was composed of a water-soluble substance (arabin) and 
a water-insoluble substance (cerasin) ; cerasin was, however, soluble in lime- 
water. These gums occurred together in an intimate mixture. Mikosch 
was able, however, to separate the arabin almost completely from the 
cerasin by levigation. When cerasin had been as thoroughly as possible 
freed from arabin it would, on the addition of alcohol, contract into a homo- 
‘geneous vitreous mass; pure arabin, on the other hand, gave a white floccose 
precipitate on the addition of alcohol, or better acid alcohol. 
Cherry gum was insoluble in 50% alcohol. In preparing sections of 
diseased material for study Mikosch cut from fresh branches, and examined 
the sections in water, or in 33 % alcohol, if they had to be preserved any 
length of time. This strength of alcohol was used for the reason that the 
gum only contracted slowly at this strength. Glycerine and water, equal 
parts, was also used when the sections were not to be kept for any great 
length of time. 
Mikosch had very little success with staining reagents. He found 
double staining with neutral red and acid green more reliable than ruthenium 
red. Chloriodide of zinc was fairly satisfactory ; the cell-walls stained blue, 
as in healthy tissue, and the gum yellow. 
The gum was produced in the young wood in formation, and the 
physiological changes leading to its formation were as follows :— 
In the central cells of the groups boxed in, as it were, between the 
cambium, xylem, and adjacent medullary rays, the protoplasm appeared 
denser than normally, was granular, and contained starch grains. Follow- 
ing very closely the increased protoplasmic content and appearance of 
starch, the diseased cells separated schizogenously, and further changes 
rapidly followed in the cytoplasm. The starch grains became transformed 
into as many gum droplets, and their remnants, when present, stained 
reddish brown with iodine solutions. The gum droplets were precipitated 
tz situ when sections were first placed in alcohol, but appeared as clear 
spots when the alcohol was replaced by water, owing to the partial solubility 
of cherry gum in the latter. Soon after their formation the gum droplets 
collected together between the protoplast and the cell-wall. If we call, for 
convenience, the apex of the cell that portion of it which is bounded 
by the intercellular space, then the gum may’ be said to have accumu- 
lated invariably between the protoplasm and the apex of the cell. Starch 
does not appear, however, to have been the only source of gum formation, 
