10 



colored. Most of the afiected pods, however, reach full size, and the 

 beans may be apparently sound or only slightly discolored at the seed 

 scar, or they may be much discolored. The whole plant does not 

 usually die outright, but lingers through the season 



If we tear out a bit of tissue from a diseased spot in the leaf, 

 crush it on clean glass, and examine it under the microscope, we shall 

 find bacteria in very great numbers ; they are so numerous that the 

 diseased tissue seems to be a mass of bacteria, and all apparently of 

 one kind— small, short rods, single, or joined end to end in twos. 

 This germ, and the disease caused by it, were first described by Erwin 

 Smith, and the name given to it is Pseudomona^ phaseoli. 



With proper care, we 

 may tear open a stem, 

 take a bit of diseased 

 tis-ue, crush it in melted 

 gelatin ; and pour the 

 whole into glass dishes. 

 Here, the gelatin be- 

 comes solid, holding each 

 germ apart from others, 

 where it grows and mul- 

 tiplies, and in four days 

 small, round, yellow 

 spots or colonies appear. 

 On examination these 

 colonies are found to 

 consist of bacteria like 

 those in the diseased 

 plant. We can now 



Fig 5-Tnebean plant inoculated with the bacillus which transplant a Colouy tO 

 • causes the disease. Showing the wilted leaves. ^^arioUS media aud ob- 



serve its growth in pure culture. By such methods, we have re- 

 peatedly got pure cultures from leaf, stem, pod and seed. The bac- 

 teria have been obtained alive from the seed coats of beans kept m 

 the dry pods or in sterile test tubes over winter, and the same seeds 

 have then germinated and grown. 



During the past winter, we have inoculated more than twenty 

 bean plants growing in pots in the laboratory. The surface to be 

 inoculated was touched with a hot platinum needle and then punc- 

 tured with a sharp, sterile platinum needle. The needle was then 



