22 
The bacteria in these cotyledons are carried by insects or, oozing out 
upon the surface, are splashed by rain to the leaves. The insects introduce 
the pathogene into the wounds which they make or the bacteria may 
enter through the stomata, thus initiating primary infection. The primary 
infections which are seldom to be observed, exhibit the same type of leaf- 
lesion as the secondary infections. The primary cycle is probably never 
completed, the bacteria in the primary lesions dying with the disintegration 
of the leaves. ‘ 
The Secondary Cycle infections are far more numerous and therefore 
are more destructive than the primary. They are the ones most commonly 
observed. They are repeated frequently throughout the season, initiated 
at first from the primary and later from earlier secondary infections. 
: Pathogenesis. The pathogene is carried by imsects or rain from 
the primary lesions to healthy leaves and pods. Examine several of 
the leaf-lesions carefully to see if you can LOCATE :— 
7. The point at which the bacteria were introduced. Was the 
inoculating agent a biting or sucking insect? Was the lesion a result of 
stomatal invasion? ; 
With a scalpel, chop in a drop of potassium hydroxide (do not erush) 
a bit of leaf-tissue from the outer opaque green zone of the lesion. Cover 
carefully and under low-power OBSERVE :— 
8. The bacteria oozing from the cut ends of the veins. Make a 
DRAWING of a vein with oozing bacteria. 
Examine several deep pod-lesions, cutting across the pod through the 
lesion or shelling out the beans. The bacteria in the pod invade the 
seed, where, with the ripening of the seed, they become dormant, thus 
completing the secondary cycle. Can evidences of invasion of the seed 
beneath the lesion be detected? 
Saprogenesis. Although there is no evidence that this pathogene 
lives and multiplies outside the living tissues of the bean, some investi- 
gators hold that it may live over winter in the stems and leaves on the 
ground (Ontario Bul. 136:12.). It will, however, grow readily on culture 
media. Examine the plate- and tube-cultures and opsERVE>—~ 
9. The color, form and consistency of both the buried and 
surface-growing colonies; effect on the bouillon-cultures. DRAW and label 
to indicate color and other characters. 
Make a mount from one of the surface-colonies and COMPARE :-— 
10. The bacteria with those studied from the tissues as to size, 
shape, cell-unions and motility. praw. 
For flagella see Cornell Bul. 239:211. copy. 
Pathological Histology. Examine the sections (freehand or prepared) 
of diseased pods, stems, or leaves. OBSERVE :— : 
11. Which tissues are chiefly invaded in the organ examined. 
12. The relation of the bacteria to the cells; within or between? 
13. The effect on the cells; on the middle lamella and protoplast. 
Make prawincs necessary to bring out these points. 
REPORT 
1. Detail the life-history of Bacterium Phaseoli EFS., describing 
the symptoms resulting from its activities in the different organs of the 
host. Follow the sequence and indicate the headings, used in this outline. 
