FUNGOID DISEASES OF POTATOES 79 



times called nailheads) varying in size, which when 

 the epidermis is scraped have a purple colour ; such 

 a tuber, if cut and placed in a moist warm atmo- 

 sphere, will develop an abundance of the fungus 

 hyphae from these spots. 



The oospores (resting spores) are claimed by 

 W. G. Smith to have been found by him in 1875, 

 but the matter remained in doubt in many quarters. 

 Recently, however, Dr. G. P. Clinton' at the Con- 

 necticut Agricultural Station, and others following 

 his methods, have succeeded in obtaining oogonia 

 and oospores in pure artificial cultures of the fungus ; 

 Pethybridge - has shown that they are identical 

 with the oospores formed by P. erythroseptica, 

 which causes pink rot of potatoes. It is still un- 

 certain whether these are ordinarily produced in 

 nature, but the fact that the disease appears to be 

 equally as bad (sometimes worse) on newly broken- 

 up land indicates that the disease is not usually 

 carried over winter as oospores in the dead leaves, 

 etc. 



Preventive Me as u res. — 



1. Plant sound seed. 



2. Plant seed of the more resistant varieties. 



3. Earth up well so as to prevent the conidia 

 from beinor washed down to the tubers. 



o 



1 Clinton, Ti^^/^rA- Coimecticut Exp. Station (191 1), and earlier 

 reports (1905-10). 



2 Pethybridge and Murphy, Sc. Pro. Royal Dublin Society^ Vol. 

 XIII. (N.S.), No. 36, March, 1913. 



