OTHER BACTERIAL DISEASES OF PLANTS. 303 
It is important to note that the bacterium that causes the brown 
rot of the potato can also live as a parasite in the tobacco plant where 
it produces what is known as the Granville unit. 
The Wilt Disease of the Gourd Family (B. tracheiphilus, Sm.). 
This bacterium attacks various members of the gourd family, being 
best known in the cucumbers, muskmelons, pumpkins, and squashes. 
The bacterium that produces it will grow readily in laboratory 
media and invariably produces the disease when it is inoculated into 
healthy plants. It causes the wilting of the plant by clogging up 
its vascular ducts. The bacteria appear to be distributed by in- 
sects which inoculate the plant, chiefly on the leaves, by puncturing 
or by eating holes in them. The cucumber beetle and the squash 
bug are especial offenders in this respect, and anything that will 
keep these insects in check will help to reduce the troubles from the 
disease. 
The Corn Wilt (Pseudomonas stewarti). This disease affects 
sweet corn in 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 
after 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 com- 
posed 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. Zea, B. cloaca). 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. 
