124 PROTECTION OF PLANTS — 1923-24 



Historical Review. 



In 1908 Ducomet published an account of a new potato disease occuring 

 in France which he called "Dartrose". This he ascribed to Vermicularia 

 varians sp., nov., which organism he stated was an 'Espece variable, evoluant 

 vers les Phoma ou inversement vers les Colletotrlchum et Gloeosporium". 



O'Gara in 1915 reported a new species of Colletotrichum on potato which 

 he found in the Salt Lake Valley, Utah. He considers it related to Vermi- 

 cularia and named it Colletotrichum solanicolum. 



Taubenhaus in 19 IG in his studies of silver scurf of potato described a 

 Colletotrichum which he regards as identical with O'Gara's organism but which 

 on a basis of priority he calls Colletotrichum atramentarium. 



Pethybridge reported a similar disease from Ireland in 1918 and in studying 

 the organism came to the conclusion that it should be called Colletotrichum 

 tabificum. 



Dickson in 1921 found a black dot disease to be quite common in Quebec 

 and the organism concerned appeared to be identical with that described by 

 Ducomet except that no pycnidia were ever found. 



Organisms used. 



In this studA' the following organisms were used. 



1. The isolation from Canadian material herein called the Quebec 



organism.. 



2. The saltation from No. 1. (see Dickson 23), herein called the 



Saltation. 



3. Vermicularia varians. Ducomet. 



4. Colletotrichum tabificum. (Hallier p. p.) Pethybridge. 



5. Colletotrichum atramentarium. (O'Gara) Taubenhaus. 



6. Colletotrichum atrovirens. (?). 



Source of the cultures. 



All the above cultures were turned over to the writer by Dr. Dickson 

 who states that he obtained them as follows: 



1. Quebec organism. 



Culture made by Dr. Dickson from Quebec material. 



2. Saltation. 



Culture made by Dr. Dickson from Quebec organism. 



3. Vermicularia varians. 



Subculture made from a culture of Dr. Pethybridge made in turn 

 from one by M. Cavadas from French material. 



4. Colletotrichum tabificum. 



Culture made by Dr. Dickson from potato material sent by Dr. 

 Pethybridge. 



5. Colletotrichum atramentarium. 



Subculture made from a culture sent to Dr. Dickson and made from 

 Ohio material by Dr. Freda Detmers. 



