Chapter X 



165 



Plant Diseases 



also reproduced its own type in inoculation experiments. This organ- 

 ism also attacked the roots and rootlets of the inoculated mangel plants, 

 on which it produced numerous characteristic, dark brown, nodular 

 outgrowths. The organism was found to be identical with S. scabies. 

 A stock culture also produced the same type of scab in inoculation ex- 

 periments. 



Growth o/: Scoh Organism 



Occurrence qzZ ^oi-oto Scab 



Fig. 34.— Influence of the hydrogen-ion concentration on 

 scab organism Cfi"om Dippenaar, 90). 



the growth of the potato 



Sweet Potato Pox or Soft Rot.— Soft rot of sweet potatoes was first 

 ascribed to various fungi. Taubenhaus (411) suggested that a certain 

 actinomyces is the causative agent of this disease. The organism, de- 

 scribed as A. foolensis, was a parasite of superficial wounds following 



