XIV. THE CROWN GALL 



(Syn. Plant Cancer) 



Type. — This also is an overgrowth, but of a different kind 

 from the preceding. Crown gall is a disease of wide geograph- 

 ical distribution, occurring on a great variety of cultivated 

 plants (Figs. 315 to 319) and on some wild ones, e.g., the chest- 

 nut. It is primarily a disease of the parenchyma but it is unlike 

 any of the diseases hitherto described in that the cells of the at- 



FiG. 315. — Crown gall on hop. Paris daisy strain. A pure-culture inoculation. 

 Time, about 3 months. April, 1907. }i nat. size. 



tacked parts are not disintegrated and killed, but on the contrary 

 are induced to multiply, the result being an imperfectly vas- 

 cularized, covered or naked, irregular, soft or hard overgrowth, 

 or tumor, composed in part at least of masses of rapidly dividing, 

 round or spindle-shaped cells of reduced size, forming a hyper- 

 plasia, which on some plants under favorable conditions may be 

 larger than the root or shoot that bears it (Fig. 320) but then 



413 



