128 



THE RESTING SPORES OF THE POTATO DISEASE. 



(CONTINUED.) 



As I have now had the fungus which causes the Potato 

 disease under close observation for the past seven weeks, I 

 send you some of the most noteworthy facts which have 

 more recently attracted my attention. 



1. The plants sent to the Royal Horticultural Society 

 by Mr. Dean on July 21, were covered with the Peronospo- 

 ra far beyond anything I had ever seen before. The haulm, 

 the leaves (on both sides alike), and the berries, were cove- 

 red. Some of these plants, after being placed on a garden 

 bed, and covered with leaves (to keep them moist), were the 

 next day one white mass with the Peronospora, 



2. The Potato fungus (as commonly seen) bears a far 

 larger number of simple spores than inflated vesicles con- 

 taining the zoospores or swarm-spores, but in Mr. Dean's 

 plants the fungus produced zoospores almost exclusively, and 

 in the greatest abundance. As the zoospore is a higher 

 development of the plant than the simple-spore, this latter 

 observation points to the unusually robust health of the 

 fungus this season. 



3. On suspendiug the infected leaves over a glass of 

 water for from twelve to seventy- two hours, the swarm- 

 spores fell in abundance (either free or in the vesicle) on to 

 the water, and there germinated. No single drop of tho 

 water could be taken up for examination without meeting 

 with the germinating spores, the threads radiating over the 

 water in every direction, evidently in quite a congenial 

 element. It brought the following fact to light, which 

 is of importance some of the vesicles which usually dis- 

 charge the swarm-spores discharged instead a thick mass of 

 mycelium ; and this cord, when it had proceeded a conside- 

 rable distance over the water, there had its contents diffe- 



