BACTERIAL DISEASES OF PLANTS 261 



CROWN GALL DISEASE 



It is now pretty well established that the widespread 

 disease of fruit trees called Crown Gall is caused by bac- 

 teria. This has recently become one of the most destruc- 

 tive maladies of trees, having been widely distributed 

 through nursery stock before its real nature was discovered. 

 This disease appears in spring as an abnormal growth upon 

 the roots of apple, pear, peach, and other trees, as well as 

 those of blackberries and raspberries and various herba- 

 ceous plants. The growth continues through the season, 

 often forming large galls of varied shapes. Ordinarily 

 the growth ceases at the end of the first season, and the 

 gall later decays and disintegrates. New galls are likely 

 to appear the next season on other roots in large num- 

 bers, damaging the root system so badly that the tree may 

 finally die. 



It is easy to see how readily soil could be inoculated with 

 crown-gall germs. If a diseased tree is planted and later 

 dug up, it is probable that millions of the spores will remain 

 in the ground. Consequently great care should be taken 

 not to set diseased plants, and if possible to get plants from 

 nurseries where crown gall is not present. 



CABBAGE ROT 



The Cabbage Rot is another bacterial disease that has 

 been carefully studied by several scientists in widely sep- 

 arated regions. The malady is especially destructive to 

 cabbages, often ruining large fields. It also attacks cauli- 

 flowers, turnips, rutabagas, and various other plants of the 

 mustard family. It has been found on Charlock, a weed 

 belonging to this family, and probably occurs upon other 

 species. 



