340 



and turn black, and the same kind of black patches appeared on the 

 stem, and a field of potatoes smitten by the disease, presented much 

 the same aspect as if the haulm had been destroyed by the sharp frost 

 of an autumnal night. And so alike was the appearance, that many 

 were deceived by it, and thought their crops were killed by the frost. 

 In a very few days from the appearance of the disease the haulm de- 

 cayed down to the ground. The tubers of the blackened plants 

 shared in the sudden destruction, their surface became discoloured, 

 and of a livid leaden hue, and the rind presented a rugose or pustu- 

 lated appearance, but the same root bore tubers both sound and 

 unsound, and in all states of disease. I did not notice that the per- 

 fection of the tuber at all interfered with the progress of the disease, 

 because fully grown and immature tubers were equally infected on 

 the same root, nor could I at all ascertain, as some have asserted, that 

 the tubers nearest the surface of the ground were first attacked. 



When an infected tuber is cut across, the circumference is disco- 

 loured, and turned brown beneath the rind ; the external portion of 

 the potato being the part first affected. The brown spots seem drier 

 than the rest of the structure, and the whole much resembles the 

 brown discoloiu'ation beneath the skin of a bruised apple. It is pretty 

 generally stated that the tubers soon pass into a state of complete 

 decay, a nioist rottenness, but this is, I think, an accidental circum- 

 stance, for if kept in a dry place, they desiccate and shrivel, at least 

 such is the case with my specimens. In a state of moist decay they 

 exhale a most unpleasant odour. Only a portion of a tuber is some- 

 times diseased, and the eyes of the sound poition germinate as usual ; 

 and if a part of the potato is above ground and exposed to light, 

 chlorophylle is formed in the tissues. When cooked, the appearance 

 of the unsound potato is very disgusting. All the portions which 

 were brown when raw, when boiled turn of an ashen livid hue, and the 

 substance of tlie whole is waxy and the odour and taste very unplea- 

 sant. There can be no doubt that these potatoes are totally unfit for 

 human food, and that eating such would be dangerous, it being too 

 well known that decayed or decomposing vegetable or animal sub- 

 stances, when eaten, produce severe diseases. 



A microscopical examination of a portion of a diseased potato ex- 

 hibits the following conditions. That portion, usually the centre, 

 which is still tolerably sound, contains the starch corpuscles in an un- 

 altered state, whilst the circumference of the tuber, which is usually 

 discoloured and unsound, will be found nearly exhausted of starch. 

 The starch corpuscles disappear, or are absorbed or disintegrated in 



