A New Potato Disease. 



321 



locality. In the inoculated pots the potatoes were very different ; 

 some in each pot were badly deformed and exhibited the disease 

 in a most pronounced form. Figure 1 is a photograph of 

 tubers grown in the experimental pots : A one from the con- 

 trol pot, B and C from the inoculated pots. 



These pots were allowed to remain, with the same soil, undis- 

 turbed until the next spring, when a second time potatoes were 

 planted in them, without the admixture of any fresh spores. 

 Those in the control pot produced normal, healthy tubers ; 

 while in the others the tumorous excrescences were again devel- 

 oped, and microscopical examination revealed the presence of 

 the characteristic spores observed in the original diseased 

 specimens. 



The parasite can thus be propagated by means of spores in 

 the soil and, when once it has been established, can maintain 

 itself over the winter and infect the crop in succeeding years. 



Judging from some sections in an early stage, the attack 

 appears to commence at the " eyes," the parasite easily gaining 

 an entrance into the outer cells of the young and tender struc- 

 tures which normally would develop into leaves. In these the 

 cells are readily stimulated to divide, and, as a result of the 

 injury caused by the parasitic invasion, irregular cell-division is 

 set up. The destruction of any one cell causes those in contact 

 with it to divide in the attempt to heal the wound ; when 

 these latter cells are attacked in their turn, a further cell-division 

 is induced, and by a repetition of the process the leaf-protuber- 

 ances become converted into an irregular cell-mass which in the 

 initial stages may be seen as finger-like outgrowths (Fig. 2). 

 From these points the irritation spreads along the cork-cambium, 

 so that the cells over a large portion of the surface of the potato 

 gradually undergo this irregular division and multiplication, 

 which is extended also into the internal tissues. 



The parasite can be seen in the diseased tissues as a globular 

 protoplasmic mass (plasmodium), destitute of cell-wall and with- 

 out any trace of mycelium. It draws its nourishment from the 

 host-cell and consumes the protoplasm and almost the entire 

 cell-contents, leaving only a brown cell-wall. The plasmodium 

 divides, part passing through the cell-wall into the adjacent 

 cells, and in this way the disease spreads through the tuber. On 



