1893.] 



MICKOSCOPICAL JOURNAL. 



159 



European countries. The other cause is Afacrosporium solani., 

 and this, in the United States, is more prevalent than the other. 

 The general outward appearance of the two is the same, and only 

 by a microscopical examination can, they be separated. As, 

 however, the effects of both are alike, and as the treatments for 

 prevention are identical, a description of the one will apply to the 

 other. Both are more prevalent on late than on early potatoes, 

 and warm, moist weather is that during which they grow and 

 spread with greatest rapidity. Both seem to appear suddenly and 

 run their course rapidly. The following remarks, while applying 

 more particularly to the Phytophthora^ will generally hold good 



Fig. I. Potato leaf affected by blight. 



for the other fungus. The sudden appearance and spread of the 

 Phytophthora has been frequently observed, and as long ago as 1S45 

 was commented upon. A twenty-acre field that on one day in the 

 last week of August was green and thrifty, on the following day 

 looked ''as if it had been exposed during the night to the action 

 of steam. Stems and leaves were soft and blackened ; in six and 

 thirty hours a few sickly stems and discolored leaves were all that 

 remained. The crop had ceased to exist." This fungus has been 

 found not to grow and produce spores at a lower temperature 

 than 34°, or a higher one than 77^. The best temperature for it 

 is 72° Fahrenheit. 



