350 AGRICULTURAL BACTERIOLOGY 



and runners wilt suddenly, as if from a lack of water or 

 from too hot a sun. The whole plant may wilt, or only 

 one runner. The disease is caused by an organism, the 

 growth of which fills the water-ducts with a viscid mate- 

 rial that prevents the rise of the water, and wilting follows. 

 If the cut ends of a vine are rubbed together gently and 

 drawn apart slowly, the viscid matter will string out for 

 some distance. 



The infection is supposed to occur through wounds in- 

 flicted by insects, such as the striped cucumber-beetle and 

 the common squash-bug. 



A similar wilt affects the egg-plant, tomato, Irish potato, 

 and tobacco. 



Galls or tumors. Another class of plant diseases is 

 marked by the formation of galls and tumors. Crown gall 

 is the most important, and is peculiar by reason of the 

 great number of plants that are susceptible to the attacks of 

 the organism. The apple, peach, plum, prune, apricot, 

 cherry, grape, raspberry, blackberry, rose, English walnut, 

 chestnut, almond, white poplar, hop, sugar-beet, potato, to- 

 mato, tobacco and Paris daisy are susceptible. The great- 

 est economic losses are in connection with fruit trees and 

 shrubs. It has also attracted attention because some of the 

 manifestations of the disease are very similar to cancer in 

 human beings. The presence of the causal organism stimu- 

 lates the surrounding plant tissue to continued and persist- 

 ent growth, which results in the formation of excrescences 

 or tumors of varying size. 



