136 "Black Neck" or Wilt Disease of Asters 



that, though the initial infection occurs in the seedling stage, the disease 

 may not be seriously manifest until late in the life of the plant. -In this 

 respect, therefore, the aster disease differs from other diseases caused 

 by species of Phytophthora where the destruction of the host plant is 

 very rapidly accomplished. 



In conclusion I should like to express my indebtedness to Professor 

 W. H. Lang for his advice and helpful criticism during the course of 

 this investigation, which has been carried out in the Cryptogamic 

 Botany Research Laboratory of the University of Manchester. 



Summary. 



1. The tissues of asters attacked by the wilt disease always contain 

 the mycelium of a species of Phytophthora ; this fungus was isolated 

 and grown in pure culture on various media. 



2. Several saprophytic fungi including a species of Fusarium 

 were isolated from the decaying roots of badly diseased asters but 

 none of these is the primary cause of the disease. 



3. A series of inoculation experiments with adequate controls 

 showed that the Phytophthora could produce a disease on seedling and 

 mature asters identical in every respect with the "Black neck" or 

 wilt disease. 



4. A similar series of inoculation experiments with the Fusarium 

 gave negative results. 



5. The characters of the vegetative mycelium and its relations to 

 the tissues of the host plant were studied in some detail. 



6. The sporangia show most of the characters described by De 

 Bary for Phytophthora omnivora, but after the discharge of zoospores 

 the stalk of the sporangium grows through and produces a second 

 and even a third sporangium within the first. This proliferation has 

 not, as far as I know, been previously described for any species of 

 Phytophthora. 



7. No sexual organs have as yet been observed either on infected 

 plants or in pure culture on suitable media. 



