May 6, 1918 CankcY of Poplars and Willows 335 



CULTURAL STUDIES 



Media. — Cytospora chrysosperma has been grown by the writer on two 

 culture media : Corn-meal and malt agars. This fungus will probably grow 

 on any of the usual media, to judge from the growth made on these two. 



Isolation. — The fungus is easily isolated by removing under sterile 

 conditions a small piece of the diseased tissue of the inner bark and trans- 

 ferring it to agar tubes. It can also be isolated by means of the pyc- 

 nospores on agar slants or by the poured-plate method. 



PHYSIOLOGICAL CHARACTERS 



Certain characters are common to the growth of this fungus on corn- 

 meal and malt agars. The most characteristic reactions were obtained 

 with pure pycnospore cultures on 2 per cent malt agar, + 7 (Fuller's scale). 



On this medium the following characters develop when streak cultures 

 are made : 



The mycelium begins along the streak as a white cottony growth which 

 spreads rapidly toward the sides of the tube. In seven days at ordinary 

 room temperature the white color of the aerial mycelium gradually 

 changes to a light buff, while in 10 days the submerged mycelium seen 

 in mass is turning black. In 16 days the aerial mycelium is cottony in 

 character and covers the entire exposed, surface of the agar slant. It 

 now varies from light buff to warm buff in the upper portion of the slant, 

 while the lower portion is turning to a neutral gray and is becoming 

 matted and adherent to the surface of the agar. The submerged mycel- 

 ium is now black in mass and shows as a very distinct and characteristic 

 border along the edge of the agar. Twenty days after the tubes had 

 been inoculated, very small pycnidia, 0.4 to i mm. in diameter, were 

 developed at the edge of the cultures next to the glass in the petri dishes 

 and test tubes which were exposed to strong, diffused light. These small 

 pycnidia contained typical pycnospores, which were discharged against 

 the glass sides of the tubes in place of into the air. The test tubes of malt 

 agar 20 to 25 days after inoculation show a very characteristic color 

 reaction when the tubes are viewed from the rear of the slant — viz, the 

 agar has retained its normal color except at the edge of the agar and air; 

 here is seen a black layer of submerged mycelium bordered above by a 

 layer of white to waim-buff aerial mycelium. 



As the cultures in the tubes grow older, much of the aerial mycelium 

 gradually becomes wet, mats together, and adheres to the surface of the 

 agar, varying from mouse-gray to black in color ; here and there elevated 

 patches of white to light-buff mycelium remain (PI. 28, C). These eleva- 

 tions are 3 to 6 mm. in diameter, hemispherical in shape, and contain the 

 pycnidia. About 30 days after inoculation large typical pycnidia mature 

 and begin discharging spores (PI. 28, C). On plate cultures of malt agar 

 this fungus has the same general characters of growth, except that the 

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