12 



urated atmosphere, where it was kept. Plant No. 2 was sprayed with 

 sterile distilled water in which spores from a pure culture of Alter- 

 naria molce had been sown, and was then placed under the same con- 

 ditions as plant No. 1. The temperature of the laboratory at the 

 beginning of the experiment — 3.30 p. m. — was about 80- F. The fol- 

 lowing- notes, made during the progress of the experiment, are descrip- 

 tive of the results obtained: 



February 14, 1896, 9.30 a. m. Plant 1 apparently in a perfectly healthy condi- 

 tion, leaves covered with moisture, but showing no ill effects from the spraying or 

 from being kept in a saturated atmosphere. Plant 2 liadly diseased, nearly every 

 leaf showing one or more spots of infection, which are in every particular identical 

 with the first stages of the disease as naturally produced. 



February 15, 1896, 9.30 a. m. Plant 1 still remains healthy and apparently unin- 

 jured by the treatment. On plant 2 the disease is progressing rapidly. There is a 

 peculiarly disagreeable odor present when the bell jar is removed that is not 

 noticeable under the same conditions with plant 1. This odor, so far as I am able 

 to judge, is identical with that noticed with plants suffering from an attack of the 

 disease under normal conditions. This odor is one of the characteristics of the dis- 

 ease, and its presence in the house, frame, or field is usually the first intimation the 

 grower has of the presence of the disease among his plants. 



February 19, 1896. Plant 1 still healthy and apparently in good condition. The 

 spots on plant 2 are a little further developed and resemble more closely those 

 produced under natural conditions. 



A striking example of the results obtained b}' artificial inoculations 

 of violets with this fungus is shown in PI. IV. The two plants shown 

 in this photograph received the same treatment as that given the two 

 plants in the experiment described. The plants were sprayed at 3.30 

 p. m., August 26, 1896, and examined first at 2.30 p. m., August 27, 

 1896, just twenty-three hours after treatment. At this time plant 

 No. 1 appeared free from disease, and showed no ill effects whatever 

 from the treatment. On the contrary each leaf of plant No. 2, with 

 one or two exceptions, showed from 1 to 30 or more spots of the dis- 

 ease, which were in every way identical with those produced on plant 

 No. 2 in the previous experiment. 



The plants were photographed August 31, 1896. At this date plant 

 No. 1 was apparently free from disease, while the disease on plant 

 No. 2 had made considerable progress and the spots w^ere gradually 

 assuming the normal colorings which are characteristic of this disease. 



In these spots thus produced a careful microscopic examination 

 demonstrated the presence of the mycelium of the fungus, and subse- 

 quent observation showed that the fungus pushed through to the 

 surface of the spots and fruited, whenever the leaf was put under a 

 bell jar in moist air, exactly as it did on spots occurring naturally. 

 The disease was again produced in health}- plants by inoculation with 

 the spores- thus formed. 



That the spots produced upon violet leaves by artificial inoculations 

 with spores of Alternaria violce closely resemble those occurring natu- 



