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24, Beneath the epidermis the layers of the cells which are 
regularly rectangular in shape.. This is the corky hypodermis. The 
epidermis and hypodermis constitute the skin of the potato. 
25. That from the hypodermis there is a rather abrupt transition 
to the larger, more globose cells of the cortex. Note that the cells of the 
cortex are filled with starch. 
Make a DRAWING of the skin and cortex of the healthy potato. 
Cut thin cross-sections (or use prepared slides) through sori of different 
ages; young and medium old. Put the sections from each into different 
watch-glasses. 
Mount the thinnest sections from the very young sori and NoTE:— 
26. Whether the hypodermis and epidermis are affected; the 
cells where the plasmodium enters are killed. 
27. The granular mass between and within the cells,—the 
plasmodium of the parasite. 
28. Any discoloration of the cells. Is there any enlargement 
of the cells? Note the starch-granules. Iodine solution will stain the 
starch-grains and make them more evident. . 
Examine the sections through the medium-aged sori. OBSERVE:— 
; 29. The hypertrophy of certain of the cells; enlarged in which 
direction? These are called giant-cells. Is the plasmodium of the patho- 
gene to be detected in any of them? Has spore-formation begun? 
30. That some of these giant-cells are divided by cross-walls 
into several smaller cells; hypoplasia occurs as well as hypertrophy. 
31. That this overgrowth of the cortical cells pushes up and 
eventually bursts through the skin. 
82. Any effect of the pathogene upon the starch. 
33. Effect on the nuclei of the host-cell. 
34. Evidences of cambial activity in the uninvaded tissues 
beneath the sorus. 
Make a pRaWwING of a section through a sorus showing the histological 
conditions just prior to spore-formation. 
REPORT 
1. Give the methods of control to be employed against this 
disease and explain the philosophy of their use. 
2. Consult the literature on club-root of crucifers and write a 
brief description of the life-history of Plasmodiophora Brassicae Wor. 
comparing and contrasting it with that of Spongospora subterranea 
(Walir.) Johnson. 
