G2 



I especia41y turned my attention to the method in which 

 the funfjus reached the tubers. The common statement is 

 that it advances down the stem or haulm and in that way 

 infects the potatoes. But I was quite sure from my recol- 

 lection that I had found diseased tubers when the stem had 

 been in good condition. And so I found it now. In many 

 cases I dug up plants in which the stem, both above and be- 

 low ground, was quite sound, though the rot was evi- 

 dent on the tubers. The infection did not travel that way. 

 Moreover, the time was too short. It seemed as if no 

 sooner were the leaves blijjhted than the disease could be 

 found on the potatoes. Evidently the infection was carried 

 by the fall of conids from the leaf and their access to the 

 parts underground. 



In support of this opinion, I found, as is well known, that: 



1. The disease spreads most rapidly in rainy weather, 

 because then the conids can be washed into the ground 

 more easily and more abundantly and also they live longer 

 in a moist atmosphere. 



2. It is uniformly the upper surface of the tuber that is 

 attacked. I do not recall an instance in which the lower 

 surface decayed before the upper. 



3. In no instance does the disease show itself at the 

 point of connection with the parent plant, as must be the 

 case had the infection traveled down the stem. 



4. The decay invariably begins in the eye of the potato 

 as though the fungus was unable to effect an entrance 

 through the skin, but could get in where the vascular tissue 

 came to the surface. 



5. The action of tlie fungus is strictly limited to the 

 destruction of the vascular tissue which it follows into the 

 tubers. Of course this destroys the life of the eye attacked 

 and the tissue adjoining it. But nowhere is the starchy tis- 

 sue of the potato in any way damaged. 



