_ STREAK OF SWEET PEAS 
This bacterial disease affects not only sweet peas but many other 
legtimes including clover. 
SYMPTOMS 
Examine the specimens provided (fresh, dry, or in liquid). oBsERVE:— 
On the stems. 
1. The streak-like lesions; color, extent, part of stem affected. 
Look for young isolatéd lesions; old lesions. How do they differ as to 
extent and color. DRAW to show variation in stem-lesions. Label to 
indicate colors. 
On the leaves and tendrils. 
_ 2. The similarity of the lesions to those on the stem. Find a 
stem-lesion that has extended along the petiole into the blade at its base. 
‘Note the reddening of the affected veins and the dead blade-tissues between. 
DRAW. 
3. Locate isolated lesions or spots in the leaf. Study carefully. 
DRAW and label fully as to markings and colors. 
On the flower. 
4. The character of the lesions on the petals. Especially striking 
in dark flowers. DRAW. 
ETIOLOGY 
The cause of this disease, long unknown, has recently been shown to be 
Bacillus lathryt Manns and Taubenhaus. This pathogene appears to 
be widely distributed in England and United States. 
Life-history. Little is certainly known of the habits of this parasite. 
It is supposed to pass the winter in the soil and decaying plant parts which 
were killed the previous year. 
The Primary Cycle is initiated about the time the peas begin to 
blossom. 
Pathogenesis. The bacteria in the soil are splashed by the rain 
upon the plants and gain entrance to the tissue through the stomata. 
Peel the epidermis from the stem of a healthy sweet pea. Mount outside 
up and OBSERVE :— 
5. The epidermal cells; their shape and arrangement. The 
stomata; numbers and structure. Draw. ‘These stomata are the infec- 
tion-courts. The bacteria in the moisture on the stem pass through the 
stomatal opening into the substomatal cavity. Here they multiply and 
by their toxic secretions kill the adjoining cortical cells. The disorganized 
juices of these cells diffuse into the substomatal cavity affording’ food for 
further growth and multiplication of the pathogene. 
Make sections through a young lesion on the stem (or use prepared 
slides). Examine and if possible pETEcT:— 
6. The bacteria in the tissues. Are they between or in the cells? 
DRaw to show the relation of the bacteria to the cells. 
Saprogenesis. Whether the pathogene is able to live and multi- 
ply in the soil is an open question. It is, however, readily cultivated 
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