334 Journal of Agricultural Research voi. xiii, no. 6 



from two sources: (i) Spores from spore horns and (2) spores from pure 

 cultures. The typical lesions of this disease were produced by both 

 methods. 



Three series of inoculations were made under control conditions in the 

 laboratory at Albuquerque, N. Mex., as follows: September 7, 191 5, 

 September 22, 191 6, and December 21, 191 6. In each series 12 plants 

 were inoculated with the spores of Cytospora chrysosperma, and 6 plants 

 were used as controls. In the first and third series all of the plants 

 inoculated with the fungus developed the typical lesions of this disease. 

 In the second series 9 out of the 1 2 plants were infected, but all of the con- 

 trol plants in each of the three series remained healthy. All inoculations 

 were made by incisions through the bark (about J/^ inch long) with a sharp, 

 sterile scalpel. The spore horns were first dissolved in sterilized water, 

 and this water was introduced into the incisions. In inoculations from 

 pure cultures, the spores used came from soft spore horns grown on the 

 surface of petri dishes. These spores were not put into water, but a small 

 quantity of the spore mass was introduced with a sterile scalpel into the 

 incision. Incisions which were not inoculated with the spores were made 

 as controls. All incisions, including the controls, were immediately 

 wrapped with wet absorbent cotton, which was left on the inoculated 

 plants for 10 days. All the plants were kept in the laboratory and watered 

 at the ground surface. The stems and tops of each plant therefore never 

 had any water on them after being inoculated. By this method all 

 chances of outside contamination were practically eliminated. 



In 10 to 15 days after the plants had been inoculated, typical lesions 

 of this disease began to develop in the shape of shrunken, dying areas 

 about 4 mm. wide at the points of inoculation, but the control plants 

 were healing normally. These lesions gradually spread until the stem 

 was finally girdled at the point of inoculation, and the upper part killed. 

 The first evidence of infection was usually a shrinking of the bark on the 

 diseased area; later, on very young twigs the diseased bark turned black. 

 Stems 6 to 12 mm. in diameter at the point of inoculation were entirely 

 girdled in from two to four months. In some instances sprouts were 

 developed below the girdled areas (PI. 28, B) on the inoculated plants. 

 In nature trees i to 3 cm. in diameter have been found which had been 

 entirely girdled and killed by Cytospora chrysosperma in one year. On 

 account of the small size (6 to 12 mm. in diameter) of the plants used in 

 the laboratory for inoculating experiments and the dryness of the air 

 indoors, the plants inoculated and killed by the fungus did not form any 

 spore horns. The fungus was reisolated, however, from the cankers by 

 taking small pieces of the inner bark at the boundary between the sound 

 and diseased areas and placing these pieces in artificial culture media. 

 Five or six weeks after the media had been inoculated with the diseased 

 bark, the typical spore horns of C. chrysosperma began to develop in 

 the tubes and petri dishes. 



