Observations on Squamosis and Exanthema of the Citrus . 1 1 1 
gum, however, sometimes coloured violet ; the latter coloured the gum 
yellow at all times. 
Prillieux believed that the starch, which is abundant in and around 
diseased tissues, plays an important role in gum formation, the main bulk 
of the gum being derived indirectly from it. 
In his study on Clasterosporium carpophilum Aderhold 1 made a number 
of inoculation experiments on cherry, apricot, peach, and plum trees with 
the view of determining the role played by this parasite in gummosis. He 
used both pot-grown plants and standard trees, and his inoculation experi- 
ments extended over the greater part of the growing season. Numerous 
inoculations were always made and alternated, with an equal number of 
witnesses, up the trunk or along the branches, as the case might be. The 
wounds were made, with one or two exceptions, small and unimportant, but 
were not protected, as a rule, from the possibilities of contamination. How- 
ever, this non-protection of the wounds did not affect the experiments, 
which proved quite decisive. The inoculated wounds always produced 
gum, which usually pearled more or less upon the surface, sometimes even 
appearing in three days ; whereas the witnesses invariably healed up 
normally. In some experiments C. carpophilum was inoculated, not into 
the cambium but just beneath the epidermis, or shallowly within the cortex. 
In these cases no gum appeared in either the inoculated or witness wounds. 
Aderhold also made one experiment on cherry in which he used Clado - 
sporium herbarum in lieu of C. carpophilum. No gum appeared in either 
the inoculated or witness wounds. 
Aderhold recorded one or two experiments in which an increased gum 
flow distinctly followed watering. He made no comment, however. 
In the section of his paper devoted to the histology of gummosis, 
Aderhold described the characteristic appearance of diseased tissues : the 
production of an abnormal wood parenchyma and its subsequent breaking 
down to form gum pockets ; the reproduction of healthy tissues once more. 
He also recorded an extensive formation of gum in the mid-rib of a cherry 
leaf, and the swelling and final dissolution of the pulp-cells of the fruit 
invaded by the hyphae of C. carpophilum . The swelling of the cell-walls 
and their final dissolution could be brought about either by the secretion of 
an enzyme, by the hyphae, or from the cells reacting to the stimulus induced 
by them. Aderhold mentioned both possibilities and accepted the former. 
In 1906 Beijerinck and Rant 2 published a memoir dealing very largely 
with the effect of stimuli on gum formation. They found that the peach 
1 Aderhold, R. : Uber Clasterosporium carpophilum (Lev.) Aderh. und Beziehungen desselben 
zum Gummiflusse des Steinobstes. Arbeiten d. biolog. Abt. f. land- und forstwirthschaftl. Gesund- 
heitsamte, ii, 1902, pp. 515, 559. 
2 Beijerinck, M. W., and Rant, A. Sur l’excitation par traumatisme, le parasitisme et l’ecoule- 
ment gommeux chez les Amygdalees. Archives Neerlandaises des Sciences Exactes et Naturelles, 
s^r. 2, vol. xi, 1906, pp. 184-198. 
