134 "Black Neck" or Wilt Disease of Asters 



grown on moist cotton wool in test tubes, with mycelium of the Phyto- 

 phthora and spores of the Fusarium as before. Here also the seedlings 

 inoculated with Phytophthora collapsed after 9 to 12 days, while those 

 inoculated with the Fusarium and also the controls remained unaffected 

 in any way. The Petri dish inoculations were repeated several times 

 and it was invariably found that the seedlings inoculated with the 

 Phytophthora showed the characteristic symptoms of the disease under 

 investigation. Sections of such seedlings always showed that the 

 collapse was due to the presence of the mycelium of that fungus in the 

 tissues. The Fusarium on the other hand never produced such effects, 

 in fact it was only possible to grow this fungus on decaying seedlings 

 or on those previously wounded. 



The stems of almost mature aster plants were also inoculated with 

 mycelium of the Phytophthora, a slight wound being made with a 

 sterile scalpel and a piece of mycelium from a pure culture inserted. 

 Controls were also wounded but not inoculated. After 10 days the 

 mycelium had progressed over one inch upwards in the tissues of the 

 stem and had produced the dark discoloration characteristic of the 

 disease. On cutting off one of these stems through the discoloured 

 region, well above the inoculation wound, and placing it in water, 

 the typical sporangia were obtained in 24 hours. It was not found 

 possible to infect older asters without previously wounding the tissues. 



Conclusion. 



No sexual organs of any kind have yet been found either on the 

 fungus grown in pure culture or upon asters at any stage of the disease. 

 All attempts to produce the oogonia or antheridia in pure cultures by 

 the methods successfully used by Clinton 1 , Pethybridge 2 , Dastur 3 , 

 Klebahn 4 and others for various species of Phytophthora have so far 

 proved unsuccessful. The characters already described appear suffi- 

 ciently striking, however, to warrant a discussion of the systematic 

 position of the fungus to which I attribute the disease of asters described 

 above. Eeference has already been made to the close resemblance of 

 the vegetative mycelium and sporangia to those of Pythium and 

 Phytophthora. A close examination of the characters of these two 

 genera reveals the fact that the main points of difference lie in the 

 modes of formation and liberation of the zoospores. In Pythium the 



1 Rep. Conn. Agric. Exp. Sta., 1911. a toe. cit. 



:! Mem. Dep. Ai/rir., India, L913, l. 

 1 Krankheiten dee Flieders, L909. 



