34-O Minnesota Plant Diseases. 



host plant, living in one cell of the host. When it forms spores 

 it develops a long tube, which reaches to the surface of the host 

 plant and throws out spores, which are provided with swimming 

 lashes and by means of these swim in raindrops or in the dew. 

 The swimming spores come to rest and invade the same or 

 other plants. A thick-coated, resting winter-spore is produced 

 inside of the host and this may carry the plant over to the fol- 

 lowing year. Diseased plants should therefore be burned and 

 cabbages should not be planted in beds in which the disease 

 has been serious. As the fungus is a water-loving plant, the 

 seed beds should be well ventilated and kept as dry as possible. 

 Too moist atmospheres should be avoided. 



Wet rot of potato 

 (Species of Bacillus). 

 Wet rot is a well known 

 bacterial disease. The 

 bacteria enter the potato 

 through wounds or 

 through the ventilating 

 holes in the skin (cork), 

 3 and when once inside, 

 ^^k they commence the de- 

 struction of the contents 

 of the tuber. Large cav- 

 ities appear in the tuber 

 containing a fluid mass, 

 with the potato starch 

 grains still intact. The 

 tuber soon becomes soft 

 and the entire center is 

 filled with a putrescent 



Fie. 172.-Bacterial rot of potato. After Clinton. maSS > fr m which tllC 



common name of wet rot 



is derived. This fluid mass is at first acid, on account of the 

 formation of carbonic acid gas, and the acid of rancid butter. 

 When, later, the decomposition has proceeded still further, am- 

 monia gas and other complex organic compounds are formed 

 which give to it an alkaline reaction. 



