Observations on Squamosis and Exanthema of the Citrus. 1 1 3 
gummosis degeneration when growing within living tissues, was regarded 
as further evidence of the activity of a cytolytic enzyme ; the ferment, passing 
out from the cells killed by the activity of the fungus, attacked both the 
living plant cells and the mycelium, transforming them into gum. 
The work of Beijerinck and Rant was more fully developed somewhat 
later in the same year by the junior author. 1 
To the stimuli inducing gummosis mentioned in the joint memoir, 
Rant made a few additions ; as causal agents he mentioned a number of 
Fungi, Bacteria, insects, chemical substances, and traumatisms. The histology 
of the disease was also described at greater length. 
Rant did not believe that the gum in the vessels was due to a degenera- 
tion of the inner lamellae of the walls, and advanced the view, perhaps 
somewhat hesitatingly, that it originated either from the decomposition of 
thylloses, which, however, he admitted never having observed, or from 
degenerating environing cells. He was of the opinion that the gum could 
originate both intra- and inter-cellularly. The intracellular gum originated 
in the manner described by Prillieux. This form of gummosis he con- 
sidered, however, unimportant, as it did not contribute to the formation of 
the exudate that appeared on the surface of diseased trees. This latter gum 
originated exclusively from the degeneration of the cambial and embryonic 
wood-cells. 
The gum cavities arose between the medullary rays. The diseased cells 
separated from one another and a certain and variable number, depending 
on the virulence of the disease, became resorbed. The cells bordering the 
gum cavities thus formed became rounded and grew out into the lacunae ; 
these ingrowing cells gave rise by division to the cells floating free in the 
gum. When gummosis was severe the medullary rays were destroyed, and 
the cambium also sometimes killed. When, however, conditions favourable 
for growth recurred and the cambium had not been affected, normal wood 
was laid down over the gum-forming tissues, which gradually lignified. 
In 1906 Mikosch 2 also published an extensive article on gummosis of the 
cherry. He found that branches of plum, peach, apricot, and almond, when 
cut into 10 cm. lengths and placed in water at room temperature, developed 
gummosis readily, and his studies were confined very largely to patho- 
gnomonic material obtained in this manner. In all the species of Prunns 
experimented with, gum readily formed in eight days, in some cases even 
earlier, and could be seen with the naked eye pearling between the cortex 
and the wood. The statement that gummosis developed to a visible 
extent was generally, though not specifically, correct. To be exact, branches 
removed in October, November, and June gummed promptly ; branches cut 
1 Rant, A.: De Gummosis der Amygdalaceae. Thesis, Amsterdam, 1906. 
2 Mikosch, K. : Untersuchungen iiber die Entstehung des Kirschgummi. Sitzungsber. d. k. 
Akad. d. Wiss. Wien (math.-nat. Klasse), cxv, 1906, pp. 911-61. 
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