11 



touched into a pure culture of bacteria from the diseased beans and 

 thrust again into the puncture. The puncture was closed and sealed 

 with a loop of sterile, melted paraffin. Other punctures were made 

 and covered in the same way but no bacteria were introduced. Every 

 inoculated plant sickened and the same symptoms developed as were 

 observed in the diseased plants in the field. Numerous check plants 

 remained healthy. Plants inoculated in the stem showed symptoms 

 after two or three weeks. At first, there is a yellow discoloration, 

 spreading slowly from the point of inoculation. As the disea'-e pro- 

 gresses, it enters the leaf by way of the leaf stalk and kills it. Finally, 

 the whole plant may be killed or it mav linger alive for month'* 



The leaf may be 

 inoculated by punctur- 

 ing the veins, but a 

 better way is to inocul- 

 ate in the petiolules, or 

 short stalks of the in- 

 dividual leaflets. The 

 disease most affects the 

 woody bundles of leaf 

 and stem, and all the 

 woody bundles of the 

 leaflet converge in the 

 petiolule. A puncture 

 in the petiolule causes 

 no lasting injury Imt 

 soon heals if no bacteria 

 are introduced. 



The needle, which 



Ihe bacillus which 

 wilted leaves. 



should be fine and sharp, Fig. 6.— I'he btjan plant inoculated with 



causes the disease. Showing the ' 



IS thrust into the petio- 

 lule from its upper end downward. Each of the three petiolules 

 is thus punctured and the culture is then introduced into one or more 

 of the punctures and all are closed with sterile, melted paraffin. 



Some time will pass before any symptoms appear. In about 

 three weeks, the inoculated leaflet droops on its stalk and wilts in the 

 sunshine, but apparently recovers at night. There is a yellowing at 

 the base of the blade ;this spreads rapidly, following the veins. The 

 aflfected tissues wilt, and the veins becomes dark brown. Within five 

 days from the appearance of the first symptoms, the leaflet is dead 

 and dry. 



