320 Diseases of Truck Crops 



dark warts, sometimes as large as the tuber itself, 

 appear on its sides or ends (fig. 6i a). The warty 

 growth consists of a scabby gall-like formation, 

 closely resembling the crown gall of the peach. The 

 last stage of the disease is when the fungus has utilized 

 all the food stored in the tuber and has reduced it to a 

 brownish black, soft mass with a very offensive odor. 

 At this stage the fungus consists almost entirely of a 

 mass of spores which, when disturbed, scatter and 

 spread all over the field. 



The Organism. Chrysophylyctis endobioticum has 

 been investigated by Johnson' and others. The 

 vegetative parts of the fungus consist first of a naked 

 mass of protoplasm which attacks and feeds on the 

 protoplasm of the cells of the host. As this bores 

 from cell to cell, it stimulates abnormal growth, which 

 results in the warts or galls already mentioned. 

 During the summer, the Plasmodium rounds up, 

 forming a thin smooth wall about itself. Later the 

 contents of this body break up into ntmierous zoo- 

 spores, which escape through a hole in the cell wall 

 and attack healthy potato tissue. As the season 

 advances, the fungus ceases to reproduce by means of 

 zoosporangia and zoospores and forms a resting spo- 

 rangium. This helps to carry the fungus over the 

 winter, and the following spring it germinates by 

 means of zoospores. 



Control. So far, there are no methods of control 

 known. It is imperative that we prevent black wart 



'Johnson, T„ The Scientific Proceedings of the Royal Dublin Soc, 

 Vol. 12, 1909. 



