11 



colonios are of difforont vari'^tics. However, if sueli plates should 

 unifonnly yield nunieroiis colonies mostly of cue sort, the evidence 

 would be favorable, but still not conclusive. 



INFKCTION EXPERIMENTS. 



Arthur and BoUey's tirst infection experiments were made with 

 rK[uid cidtures developed from cutting up diseased leaves into nutrient 

 Ihiid. When the liuid became cloudy '•application of the li({uid was 

 macU' with a camel's hair brush to the surface of four young U'aves of a 

 a small, healthy carnation plant growing- in a greenhouse." After fifteen 

 days indications of change were detected in the infected region, and in 

 nineteen days the characteristic dots were seen where the infusion was 

 api)licd. "the remainder of the plant remaining quite free from any 

 such appearance." Another plant, covered by a l)ell jar, was similarly 

 treated a few days later, and in seventeen days showed distinct evi- 

 dences of the disease. Nothing is known with regard to thc^ organisms 

 which this culture may have contained. 



After the isolation of the yellow germ described, many surface 

 infections were tried, but, according to the authors, "the purity of 

 the cultures could not always be guaranteed, or else the trial plants 

 developed diseased spots outside the inoculated area and thus absolute 

 certainty could not be obtained." The investigators named make the 

 following statements in regard to their infection experiments: 



January 15, 1890, an infection of three seedling carnations in the greenhouse, two 

 protected with hell jars and one uncovered, was. made as previously described, using 

 a potato infusion. This infusion had been infected the day bef(jre with the yellow 

 coccus-like germs from a pure culture on solid media, which had originally been 

 obtained from diseased carnation leaves on November 18, 1889. The affected areas 

 began to show disease in six days, and in eleven days more all the leaves became 

 "infected at the points of application, and at these points only," as stated in the 

 record book, and remained so for a month and a half or more. It was now believed 

 that the germ causing the bacteriosis was found, and although many subsequent 

 infection experiments were carried out with varying success, the remainder of the 

 winter was chiefly given up to the biological study of the specific germ. 



The l)est method for applying the contagium was for a time Tincertain. The 

 method used in studying pear blight, the well-investigated liacterial disease of ponia- 

 ceous trees, which consists in abrading the surface so that the germs may at once 

 come in contact with the internal juices and tender tissues of the plant, proved inap- 

 plicable to the carnation disease. No clearly marked cases of the disease were 

 obtained in this way. The wounds showed in some cases a slightly yellowish mar- 

 gin, but otherwise gave few indications of results differing from those which might 

 arise from accidental abrasions. 



Surface application (wetting the uninjured surfaces of the young leaves with the 

 germ-laden fluid) was finally adopted as the proper method of infection. Experi- 

 ence showed that success could only rarely be attained when the infectious fluid was 

 applied to mature leaves. The best results were always secured when the application 

 was made to the small appressed leaves at the end of the stem. They were drawn 

 back and well wet with the fluid, and if growing vigorously usually showed the 

 characteristic pellucid dots by the time the leaves were full size. A difficulty was 



