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DRAW to show these points and the relation of the bacteria to the cells. 
Examine the prepared longisections through the advancing margin 
of the lesion and see if it can be DETERMINED ‘— 
21. Just where the diseased cells leave off and healthy ones 
begin, On what characters are the conclusions based? What tissues 
are affected? 
22. How the cells are separated from one another, Relation 
of the bacteria to the separating cells. 
DRAW to show the cell-structures, dissolving middle-lamella and bacteria 
at the advancing margin of the lesion. 
Pathogenicity studies. To give the student some idea of the rapidity 
with which the bacteria destroy tissue, a simple inoculation experiment 
may be made as follows:— 
(a) Cut three short pieces of healthy leaves of iris, cabbage or cauliflower 
and three thin slices of roots of carrots or turnips and place them in clean 
petri-dishes on wet filter-paper. (b) Flame a needle and puncture one 
piece of each; these constitute the checks. (c) Flame the needle and 
when cool, draw the point through the pure culture and then puncture 
a second piece of each. (d) Flame the needle and when cool, draw the 
point through the soft diseased tissue and puncture the remaining pieces, 
Label carefully and set away until next exercise when they should be exam- 
ined. Record by sketch or description the results of the experiments. 
The instructor will demonstrate the method of isolating the pathogene 
to get it in pure culture. 
REPORT 
1. Describe and explain in detail the pathological effects of 
Bacillus caratovorus Jones on susceptible plant-tissues. 
