130 



like the larva of the dragon- fly), the Peronospora somewhat 

 analogous with the perfect butterfly, and the resting-spore 

 with the chrysalis. 



5. I find by experiment, when badly diseased haulm 

 and fruit is partly submerged for from one to four days, the 

 Peronospora changes its character, and produces the Pythi- 

 um or Saprolegnia-like growth on the submerged parts. 

 On examination of the plants this may be easily overlooked, 

 as the Saprolegnia commonly frees itself and floats on the 

 surface of the water, and must be carefully taken off (invi- 

 sible as it is) with a camel-hair pencil. If the oogonia now 

 produce zoospores in the water, as in Pythium, which is 

 possible and even probable, it in no way invalidates my 

 views, or makes the connection less probable between a 

 true Pythium and the Peronospora. 



6. The aerial spores of the Peronospora never become 

 globular in water, whilst the oogonia and antheridia are 

 -always so. . 



7. A superabundance of water excites the growth of 

 the mycelium, but it retards the proper production of the 

 resting-spore, just as a superabundance of water in most 

 plants makes leaves and retards flow ers. 



8. In my calendar of the weather I find we had here 

 only five wet days from May 7 to June 10 (no wet between 

 May 8 and 20), and it was during this dry weather that the 

 potato fungus this year lived inside, and at the entire ex- 

 pense of the plant, and there perfected its resting-spores. 

 With the twenty- two wet days after June 10 the Peronos- 

 pora put on its usual shape, and came to the surface. 



9. I have got my most abundant materials from the 

 tuber when soft and almost transparent, like painter's size ; 



. in this state the starch is utterly destroyed, and, what is 

 most curious, there is no offensive smell. The tuber fre- 



