648 Journal of Agricultural Research voi. xui, no. u 



times slightly sunken. If the spread has been rapid, the color is a good 

 brown, sometimes tinged with red, extending over a majority of the ex- 

 posed surface, and sometimes over all of it. On some varieties the 

 entire exposed surface does not become covered, but spots 3 to 4 mm. in 

 diameter grow to be the largest, while new spots are constantly appear- 

 ing. Often small spots coalesce into larger ones, giving them an irregu- 

 lar shape. Eventually this spotting may appear on the underside of the 

 pod, but always in lesser quantity. From these spots no organism has 

 been cultured or observed. 



EXPERIMENTAL WORK 



From August 15 to September 15, 191 7, the average maximum tem- 

 perature was 27.2° C. at the experiment station at Greeley. No extremes 

 of weather were experienced. There were four partly clouded days; 

 rain fell three times in small amount. At this altitude (4,700 feet) the 

 days during this period were v/arm and clear, and the heat of the sun 

 seemed very intense. 



In those varieties which early showed the lack of water the disease was 

 apparent by August 20. On September i some beans of the Green 

 Bountiful variety showed spotting. Plate 64, A, shows six bean pods 

 which were exposed to the sun naturally on the plant and had become 

 well spotted. Plate 64, B, shows the reverse side of the same six pods, 

 but only faint indications of spotting appear in slight amount. 



On September 6 experiments were begun in a field of the Bountiful 

 variety.^ A small table was constructed of four stakes and a mushn sack 

 so placed that one edge came close to a number of bean pods. Pods 

 showing no spotting, and still naturally attached to the plant, were laid 

 on top of the sack, exposed to the sun. Other pods from the same stalk 

 were sUpped through a sHt made in the edge of the sack in such a manner 

 that the lower sheet of the sack supported the pod in approximately the 

 same position as the exposed pod, while the upper sheet covered it. This 

 gave each pod practically the same conditions and position, except that 

 one was covered with a single covering of thin muslin. All shading 

 leaves were removed, and the table was exposed to the full strength of 

 the sun's rays. Early in the morning the muslin was wet with dew, and 

 any spores or bacteria which might have infected the exposed bean pods 

 had an equal or better chance for contact with the covered one. 



Spotting quickly appeared on the exposed pods, while none appeared 

 on the covered ones. On September 13 the experiment was discontinued, 

 and a photograph taken (PI. 65, A). The pod which went through the 

 experimental period covered is shown at the right, removed from the 

 sack; there is complete absence of spotting. The pod at the left was 

 exposed in the position shown, and is characteristically spotted. The 

 results of seven trials were identical in every way. 



' The Bountiful variety should not be confused with the Green Bountiful variety used above. 



