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_ Cut thin sections of tubercles. Examine the central bacterioidal region 
with the high-power. OBSERVE :— 
7. The numerous infection-threads extending from cell to cell. 
This shows how new cells, formed by the primordial meristem, are infected 
from the adjoining bacteria-filled cells. 
8. The immense number of bacterioids in each invaded cell. 
9. That they are for the most part not rod-shaped like the indi- 
viduals in the soil, but are club-shaped to Y-shaped; most evident in the 
central cells. As the organisms in the host-cells or in old cultures cease 
to divide, they gradually take on these so-called involution-forms. (See 
Virginia Ann. rept. 1909-1910 :136-137.) : 
Some of the individuals in the outer cells of the bacterioidal tissue remain 
active and rod-shaped. The degenerate bacterioids are attacked by the 
enzymes of the host, and the nitrogen stored within them is made available 
for the growth and development of the host. 
Saprogenesis. With the death and disintegration of the tubercle- 
tissues at flowering-time of the host, the active rod-shaped bacteria in the 
gall are set free in the soil. Whether during their sojourn in the soil, 
they lead an active saprophytic existence, though highly probable, is not 
certain. They can be readily grown on artificial media. They are not 
known to produce spores. 
Pathological Histology. Longitudinal sections of tubercles and normal 
root-branches are provided. Examine and OBSERVE:— ° 
10. The general shape and appearance of the longitudinal 
section of the tubercle. Compare with that of the young lateral root. 
11. The kind of tissues from which the tubercles and the roots 
respectively arise. 
12. The vascular strands. Note their condition at the base 
of the bacterioidal region and the arrangement of the xylem and phloem. 
Compare with the condition in the young lateral root. 
13. The primordial meristem and root-cap. Are they present 
both in the tubercle and in the lateral root? 
14. The cortex. Is it continuous with that in the root? 
15. The epidermis. Is it present in the tubercle as well as in 
the lateral root? 
16. The bacterioidal region. Where is it located in the tubercle? 
Note the size and contents of the cells. Note the outer cell-layer limiting 
the bactericidal region,—the starch-sheath. 
What metaplastic conditions predominate in the tubercle, hypertrophy 
or hyperplasia? 
Make a diagrammatic DRAWING of a longitudinal section of a root- 
tubercle; similar comparative DRAWING of the lateral root. In these 
drawings only an outline need be made to indicate the comparative shape 
of the lateral root and the tubercle, and to locate the various tissues men- 
tioned above. 
Examine the prepared cross-sections of the tubercles. OBSERVE >— 
17. The bacterioidal region, ring of bundles, cortex and starch- 
sheath. DRAW. 
