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 wilt. 



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. Ze&, B. cloacce). 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. 



