266 Wisconsin State Hoeticultubal Society. 



sections of healthy and diseased potatoes and tested the power of 

 contagion by planting them together. Duplicate sets of the 

 tubers were thus prepared : one set was placed out in the open 

 field ; the other in pots and tubs, where there was sufficient soil 

 for the strong development of a healthy plant, but which would 

 lessen somewhat the vigor of the growth. As stated before, of 

 those set in the open ground, part decayed, part were injured, and 

 in others healthy and diseased stalks and tubers were mixed in 

 the same hill, but every one that was planted in the confined soil 

 rotted down. 



A microscopical examination of the tissues of the infested plant 

 reveals the fact that a change has taken place and is going on in 

 the organic elements there, and that it is not confined to the 

 parts where fungus growth is found, but is also seen in advance 

 of it. In a healthy plant there are hut few starch grains seen in 

 the cells, but where the potato rot is present there is a great 

 increase in their number, and often the cells are crowded with 

 them. It hardly seems probable that the presence of fungus can 

 produce starch, but it appears a far more reasonable explana- 

 tion to attribute the change to a disordered circulation, a loss of 

 vitality in the cellular tissues of the plant, preventing the normal 

 elaboration and assimilation of the sap, and that it is owing to 

 this condition of the plant that the growth of the fungus is made 

 possible. 



The following chemical analyses made by Professor Jellett, of 

 Dublin, may be of interest in this connection. Tubers in four 

 different conditions were taken, both in the natural, green state 

 and dry. I, the healthy tuber ; II, the sound part of a tuber 

 in which a small point at the other end had been just touched 

 with the disease ; III, the apparently sound part of a tuber 

 where the disease had made some progress, but was not visible to 

 the unaided eye; and IV, one where discoloration was just 

 becoming visible : 



