POTATO DISEASE. 95 



they were not treated with fungus spores, and that they invariably 

 remained healthy. 



De Bax'y describes the precautions which are needful to be ob- 

 served in order to find the Peronospora in every potato that is infected 

 with the I'ot. The diflSculties in the microscopic examination of the 

 diseased potato have prevented many skilled observers from trac- 

 ing the disease to its true cause ; but with proper care it is easy to 

 demonstrate beyond all question that where this fungus is, there is 

 potato disease, and where the disease is, there is this fungus. 



We must reserve for another article an account of the means to 

 resist the ravages of the Peronospora infestans. 



Sheffield Scientific School, of Yale College, Jan., 18G3. 



Having given an account of the potato fungus, Peronospora in- 

 festans, and described the experiments and observations which 

 have been adduced as evidences that it is the cause, and not a result 

 of the potato rot, we may now turn our attention to an important 

 question that presents itself, viz : How is the existence of the 

 fungus continued from year to year ? This point appears to have 

 been thoroughly investigated by Dr: De Bary. He describes at 

 length the researches which conduct him to the following results : 

 1st. The spores or seeds of the fungus cannot survive the winter 

 either on the dry potato top or in the soil. 2d. The Peronospora 

 infestans is not developed from the spores of any other form of 

 fungus. It happens that some fungi are propagated by two or 

 more distinct kinds of spores, some of which may be kept in the 

 dry state indefinitely, without losing their vitality. It was hence 

 necessary to examine most carefully the habits and development of 

 all the fungi, which usually occur on potatoes. The result of such 

 study is that none of them have any generic connection with the 

 potato fungus. This feeds upon the sound potato, the others feed 

 upon the decayed potato. 3d. The Peronospora infestans winters 

 in the tuber in the condition o{ mycelium,* and is carried into the 

 field in seed potatoes. We have not space here to detail the evi- 

 dence in favor of these conclusions, but must refer to De Bary's 

 work. With regard to the last, however, it may be remarked that 



! 



* The sterile fungus which yields no spores. 



