POTATO DISEASE. 91 



Some thouglit the potato had " run out," had lost its original vigor 

 of constitution from long cultivation, and thus fell an easy prey to 

 parasites that could do no damage to a healthy plant. Others said 

 that the long-continued propagation from the tubers (buds) had 

 undermined the health of the potato — like breeding in-and-in had 

 developed a kind of scrofula — and the plant must be reproduced 

 from the seed, which was done without such success as would be 

 needful to sustain that theory of the disease. 



Some thought too high feeding, especially of nitrogenous man- 

 ures, spoiled the potato. Others ascribed the disease to absence 

 of salt. Others to bad, wet weather, wet and warm weather stag- 

 nating the juices. Others thought the potato rot was connected 

 with cholera, with want of ozone, &c., &c. 



All these theories were sustained by various arguments and facts 

 but none of them explained everything, and the wisest were bold 

 enough not to know what the true cause might be. Then, as to 

 the remedies, every day brought forth the cure, but no one cured 

 twice. 



At last the genuine cause has appeared, and what is it ? Why, 

 the fungus ! But we gave that up years ago ! Well, we must 

 take it again ; it is the true cause ! Beyond all reasonable doubt, 

 it is proved that the potato never rots without the fungus, and that 

 it always rots with it. Planting the fungus on a sound potato 

 develops the disease. Shielding the potato from the fungus pre- 

 vents the disease. The rot starts where the fungus begins to 

 grow. Each microscopic cell of the tuber becomes discolored and 

 rotten, when, and only when the fungus issues its branches into it, 

 or into its immediate neighborhood. Constitution, tuber, propaga- 

 tion, aphides, salt, manures and weather, have nothing to do with 

 the disease, except as they favor or destroy the fungus. 



This is a grand result if true. After carefully studying the 

 evidence, it is hard to reject the doctrine. Let us examine the 

 evidence and judge for ourselves. 



As is well known, the first indication of potato disease is the 

 blight of the leaf. This comes on so suddenly and often so pecu- 

 liarly, as to point with the utmost directness to a fungus as its 

 cause. That a fungus is developed on and in the blighted leaf, is 

 perfectly understood, and has been from the first. To prove that 

 this fungus invariably precedes, and is immediately followed by 

 the blight, is the capital achievement lately made by Dr. Speer- 



