302 BOTANICAL GAZETTE [OCTOBER 
numerous bacteria which were produced in small colonies in the 
tissue. The general nature of the knot and the close botanical rela- 
tionship of the oleander and olive immediately suggested to him that 
the trouble might be caused by the same organism that produces 
the so-called knot or tuberculosis of the 
olive. The subject was assigned to the 
writer for further investigation, The work 
for the most part was done at the bacterio- 
logical laboratory of the University, and 
thanks are due to C. M. Harinc and Pro- 
fessor A. R. Warp, of that laboratory, for 
their courtesy and suggestions during the 
investigation. 
The olive knot is a disease of the 
branches and leaves of the olive tree. 
It occurs in Egypt, in the olive- 
growing sections of Europe bordering 
on the Mediterranean, and is also 
found in California where the olive is 
grown. The disease has been known 
for many years and is even described 
by Roman writers; but its bacterial 
origin has only been recognized since 
1886, when the organism was dis- 
covered by ARCANGELI (1) and 
SAVASTANO (2). It is found in the knots 
in what may be called colonies. These 
appear as clearer or more transparent spots 
in the callus-like tissue. These growths 
See fee have their origin near the cambium layet 
Fic. 2—Leaves of ole. and at length become darker in color. 
ander, showing knots from About this colony hypertrophy of the tissue 
ee takes place, as a natural effort of the plant 
to heal the injury caused by the bacteria. This same process of 
healing would take place in mechanical injuries. The result is 
that much soft, spongy tissue is formed that makes a rather 
favorable place for new bacterial growth, which means a new 
: 
H 
| 
