38 CAUSE AND NATURE OF CROWN-GALL 



increase in size and others originate in the newly formed paren- 

 chyma. The centers of these growths ultimately become most 

 curiously twisted nodules of tracheides and woody fibers (Fig. 

 1 8). These nodules in their early growth are entirely sur- 

 rounded by meristem tissue, and this tissue is in turn surrounded 

 by parenchyma ; thus it is entirely isolated from all other tissue 

 of like nature. Frequently as the gall decays hundreds of these 



Fig. 17.— Photo- micrograph of a section through a young gall, showing isolated 

 woody nodules surrounded by meristematic tissue in a ground tissue of large, thin- 

 walled parenchyma (X 130). 



intricately twisted nodules may be broken from its outer portion, 

 while with galls that have been a long time in forming the 

 centers of growth unite and form an irregular contorted mass 

 throughout the interior of the gall, and as a result it becomes 

 hard and woody. The rapid growth from these centers just 

 underneath the surface of the gall gives it its characteristic 

 nodular or warty appearance. 



