260 



Bush-Fruits 



they look something like the black 

 knot in plums, but are seldom so 

 dark in color. In Germany the dis- 

 ease is known as "Wurzelkropf." It 

 has ruined thousands of trees in dif- 

 ferent parts of the United States and 

 is one of the dreaded enemies of the 

 nurseryman and orchardist. The 

 cause of the malady was long in 

 doubt, it having been attributed to 

 eelworms, slime-moulds and other 

 agencies at different times in the 

 past. It is now believed to be a 

 bacterial disease. It is found on 

 daisy, poplar, rose, peach, apple, 

 raspberry, blackberry, and many 

 other plants. It is either due to the 

 same or closely related organisms, as 

 in the case of the legume bacteria. 

 It is the same disease whether on 

 the roots, stems, branches, or at the 

 crown of the plant. The bacteria 

 live within the cells of the plant. 

 Galls are most readily produced in 

 soft, growing tissue and especially 

 wherever wounds or injuries occur. 

 This doubtless led to the belief at 

 one time common among nursery- 

 men, that the swellings were simply 

 due to injuries of different kinds. 

 The disease has been very carefully 

 studied by the Bureau of Plant In- 

 dustry at Washington. Many cross 

 Fig. 38. Root-gall of raspberry, inoculations were made, as from 

 peach to raspberry, blackberry, and the like, and even from daisy 

 to many other plants. The beginning of the gall could sometimes 

 be detected as early as the fourth day after the inoculation was 



