20 
on nutrient media where it can be better studied than in the tissues of the 
host. Examine the plate-colonies of Bacillus lathryi. OBSERVE :— 
7. Their form, size, color and consistency. DRAW. , 
Mount a bit of one of the colonies in a drop of water. Cover and 
OBSERVE :-— 
8. The size, shape, motility and cell-unions of the bacteria. 
DRAW; and copy also from Delaware Bul. 108:22, fig. 1. 
Secondary Cycles originate from bacteria oozing from the primary 
lesions and spattered by rain to nearby leaves and stems. They do not 
differ in any other way from the primary. 
Pathological Histology. Study the prepared sections (cross- and longi- 
sections) through lesions on the stem. OBSERVE:— 
9. That at first the bacteria occupy the intercellular spaces, 
adjacent to the substomatal cavity. 
10. That these soon break down the cell-walls and invade 
the cell-cavities. (See Deleware Bul. 108, pl. I.) To what is the color 
in the lesion due? 
11. That not all the tissues of the stem are invaded. Determine 
which. Show this in a pRawING of the section through the stem-lesion. 
Pathogenicity Studies. Under the direction of the instructor the 
student will, if fresh material is available, make isolations from stem- 
lesions on nutrient agar or potato-agar in a petri-dish. Set the petri-dish 
away until the next exercise at which time compare with the pure culture 
studied above. 
If growing sweet peas and clover are available, inoculate under the 
direction of the instructor, with these pure cultures of the pathogene. 
Examine the plants after two days and again later for evidences of infection. 
Record in your notes the length of the incubation-period. 
REPORT 
_ 1. Describe fully how the pathogene was isolated, character of its 
growth in the media used, how the inoculations were made and the results. 
