1905. J DISEASES OF THE POTATO IN CONNECTICUT. 1 3/ 



as do some, that the fungus passes down the stems to the 

 tubers. So I see no reason for pulling up the vines to prevent 

 the tubers rotting from this trouble. The tubers, however, do 

 become infected with the fungus, apparently by the spores fall- 

 ing from the leaves to the ground and washing down on them. 

 After gaining entrance to the tuber the fungus causes a slow, 

 dry, reddish-brown rot. Bacteria and the Fusarium fungus, 

 however, often gain entrance as the result ; the blight infection 

 and these agents make the trouble much more serious. A 

 tuber containing the blight fungus often shows a pitted surface, 

 has a reddish tinge, and the skin may often be easily separated 

 from it, while in cross section the reddish-brown diseased tis- 

 sue usually shows most prominently in a band at the surface. 

 So far as we now know the blight fungus is perpetuated only 

 by the mycelium carried over the winter by these infected 

 tubers. Just how the disease is transferred from these to the 

 leaves is not definitely known, though it is believed by some 

 that the mycelium passes from the tubers up into the stems 

 and leaves. Personally I do not believe this occurs. Theoreti- 

 cally the fungus should possess thick walled resting spores to 

 carry it over the winter. Such spores have been found in 

 decaying tubers and leaves and associated with the' blight fun- 

 gus, but their real relationship has never been definitely proved, 

 and botanists are disinclined to believe that such a stage exists. 

 The writer has recently been striving to settle this point, but so 

 far has found little that is new to add to our knowledge of the 

 fungus. Artificial cultures of the fungus have been grown 

 on sterile media in test tubes. Slices of potato taken from the 

 interior of the tubers under conditions to exclude bacteria and 

 spores of fungi and inserted into a sterilized test tube contam- 

 ing a plug of cotton saturated with water have afforded the 

 best substance for the growth of the fungus. These slices of 

 potato are not decayed by the fungus, thus showing that the 

 decay in nature is due to the bacteria and other fungi which 

 closely follow the blight fungus. So far only the summer spore 

 stage of the leaves has developed in these cultures. 



The blight fungus decreases tUe yield of potatoes in two 

 ways. First, by the premature killing of the vines a month or 

 six weeks before they should die, the possible yield is dimin- 

 ished sometimes by half, as it is during the last weeks of the 

 plant's natural life that the tubers rapidly make their growth. 



