OTHER BACTERIAL DISEASES OF PLANTS 327 
sweet cornin the early summer. The leaves wilt without apparent 
cause and the plant gradually withers and dies, at times in four 
days and at others as much as a month is required. Sometimes 
the attacked plants will recover. Usually the leaves are affected 
one alter another, but sometimes the whole field seems to be 
attacked at once. If the stem is cut lengthwise the vascular 
bundles will appear as yellow streaks, which become black in the 
dead stems. If cut across, these bundles exude a yellow viscid 
substance that is composed mostly of bacteria that are the agents 
that produce the disease. The germs are thought to be distributed 
by the seeds of diseased plants, and no remedy has been suggested 
except to select resistant varieties of corn, and to use care not to 
plant seed from infected plants. 
While this bacterium attacks only sweet corn, there is another 
species that injures field corn. This has been variously named 
(B. Zee, B. cloace). It causes quite a different type of trouble, 
producing dark purplish discolorations on the leaf sheath, giving a 
yellow coloration to the plant and causing the ears to undergo a 
moist rot. It also attacks the broom corn. 
A wilt of the sugar-cane is produced by Pseud. vasculans. 
The Bacterioses and Rots.—A single illustration of this type 
must suffice. 
The Fire Blight of the pear, quince, apple, eic. (B. amylovorus) .— 
This bacterium attacks various members of the apple family and 
a number of other plants as well. The disease has been known 
for over a century and almost every conceivable explanation has 
been given for it. That it is caused by a bacterium has been 
finally demonstrated by the isolation of the organism and the 
reproduction of the disease by inoculation experiments. In the 
form known as the twig gall, the first indication of the disease is 
commonly seen in a browning or blackening of the leaves of the 
young shoots, which soon die. It then extends into the stem 
by the way of the inner bark, causing it to become blackened. 
The whole of this tissue is destroyed by the bacterium, causing a 
