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early decay of affected tissues, they may cause secondary infections on 
roots of the same or later-planted hosts throughout the season. That this 
commonly happens appears certain. The phenomena are the same as 
those of the primary cycle. 
Pathological Histology. Make freehand sections of a small healthy 
root (or use prepared slides). With low-power, OBSERVE :— 
13. The core of the root, made up of alternating wedges of 
xylem (vessels and wood-cells) and medullary rays. Note that the xylem- 
wedges are frequently fused toward the center of the stele so that the medul- 
lary rays are seldom continuous from the cortex to the center. 
Stain the section with a solution of iodine and NoTE:— 
14. The yellow color taken on by the walls of the wood-cells 
which, with their thicker walls, are now more sharply contrasted with 
the medullary ray-cells. 
15. The bark of the root surrounding the xylem-cylinder con- 
sisting in large part of the thin-walled cortex-tissues. 
16. The groups of thick-walled sclerenchyma-cells in the outer 
cortex, stained deep yellow by the iodine. What is their function? 
17. The ends of the phloem-strands, made up of small thin- 
walled cells in the inner cortex, each opposite a xylem-wedge. - 
18. The outermost tissues of the root, rough and torn,—the 
cork-layer. 
Make a diagrammatic DRAWING three inches in diameter showing 
the anatomy of a healthy cabbage root as seen in cross-section. Make an 
enlarged and detailed prawinc of a V-shaped portion of the cross-section 
showing form and arrangement of cells from center to circumference. 
Include (in outline) at least one vascular wedge. 
Cut, mount and study a thin cross-section of a diseased root (or use 
prepared slide). OBSERVE :— 
19. The abnormally increased diameter of the root. To what 
does this seem to be due; increase in size (hypertrophy) or numbers 
(hyperplasia) of the cells or both? (Compare with the section of the 
healthy root.) 
20. The xylem-vessels in a few small groups. Note their isola- 
tion. To what part of the section are they chiefly confined? Why? 
(Compare Vermont Bul. 175, fig. 3.) : 
21. The ends of the phloem-strands composed of small regular 
cells arranged in-rows around the outer end of the xylem-wedge. The 
relatively large amount of phloem, as compared with the amount of xylem; 
as compared with the amount of phloem in a bundle in the healthy tissue. 
22. The abnormally broad medullary rays, resulting from the 
increased size of the cells. The dark masses in some of the cells,—the 
plasmodia or spore-masses of the parasite. 
23. The cortex; the most abnormally increased of all the tissues. 
The cells are enlarged and perhaps increased in number. Some of them 
are filled with the brown masses of the parasite. Most of them show 
nucleus and cytoplasm. Note the entire absence of sclerenchyma or 
stone-cells; why wanting? 
24. The layer of cork-cells on the outside. Are they affected? 
Make a diagrammatic DRAWING showing the anatomy of the diseased 
root as seen in cross-section. 
