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The Disease. — The organism causing the Wart Disease of Potato gains 

 entrance to the tuber at the "eyes." In a mild attack the "eyes" turn gray and 

 then black, but in more severe cases wrinkled warts or nodules appear on the 

 surface. These are green or white at first, becoming brown or black, and may 

 convert the tuber to a brownish black soft mass, with a putrefactive odor. 



Reproduction. — There are two kinds of sporangia (spore cases) — Summer 

 Sporangia and Winter or Resting Sporangia. Summer Sporangia are formed 

 in the cells of the tuber in which the organism feeds. The spores from these 

 spore cases are set free during the summer and may at once attack other tubers, 

 thus spreading the disease. In late summer and autumn the Winter or Rest- 

 ing Sporangia are formed. These have the power of resisting winter conditions, 

 and in spring they set free a large number of motile spores. If one of these 

 spores reaches an " eye " it makes its way into the tissue and starts the disease. 

 The Winter Sporangia retain their vitahty for many years in the soil. 



Microphotograph of a small diseased nodule showing numerous resting sporangia lying closely on the surface. 



As Mr. Giissow has shown, the danger lies in the importation of potatoes from 

 infested regions, as it is impossible to detect the disease in its early stages On 

 his advice the importation of potatoes in Canada from regions known to have the 

 Wart Disease is prohibited. 



