Diseases of the Potatoe. 31 



which, as the disease progresses, run together into larger 

 spots. In these places the skin seems thicker, and has the 

 appearance of having been rubbed against something. Sub- 

 sequently, the tissue of which the skin is composed becomes 

 loosened and torn ; and by the breaking up of its continuity, 

 it assumes the appearance of the back of an old tree. Some- 

 times the skin is split up into distinct patches, like scales ; at 

 the commencement of the disease the interior of the tuber 

 does not suffer ; but, at last, a change of color takes place in 

 the tissues under the spots of the skin. Patches of a yellow, 

 or brown color, are observed, which are at first isolated, but 

 at last run into one another. These patches are drier than 

 the surrounding tissue ; but up to this period in the appear- 

 ance of the disease, no changes have taken place that render 

 the tuber unfit to eat. 



As the disease advances, little warts, or excrescences, form 

 on the skin, which are of a dark color inside ; they are at 

 first small, but keep on extending, and at last run one into 

 the other. From the surface of these warts, a fungus, be- 

 longing to the mould of the potatoe tribe, is observed to pro- 

 ject. The potatoe now begins to emit a disagreeable odor? 

 and its physical character is greatly changed. Its specific 

 gravity, which, in a state of health, is 1.163, becomes succes- 

 sively reduced, as the disease proceeds, and at last is about 

 0.9. If potatoes are planted with this disease, in no case do 

 they put forth healthy shoots. In the commencing stages, 

 the eyes put forth shoots which rise above the ground, but 

 soon perish. In the latter stages the whole tissue of the 

 potatoe is involved in disease, and on cutting into it, it pre- 

 sents a dark colored, disorganized mass, very dry, and not 

 unlike the appearance of a truffle. 



On examining the tissues under a microscope, it will be 

 found that the cellular tissue of the skin has lost its trans- 

 parency, and become of a brown color, and that of the in- 



