PLATE C 

 Camera-lucida drawing of diseased tissues of the Irish potato: 



I. — Tranverse section of an internal phloem group showing initial stage in formation 

 of intercellular spaces. (Compare Plate 38, C.) 



2. — Tranverse section of external phloem and pericycle showing the same condition. 



3. — Transverse section of interfascicular region of mature stem showing necrosis 

 in xylem, cambium, medullary ray cells, and cortex. 



4. — Transverse section of external phloem. The cells of the phloem are filled 

 with a granular deposit, yellow in color. Below these cells is seen a large inter- 

 cellular space filled with a secretion plastic in nature. 



5. — Transverse section of internal phloem of mature stem, showing severe necrosis. 

 Note that a few cells in a group are not diseased. (Compare PI. 44, A, B.) 



6. — Transverse section of internal phloem group, showing formation of a large inter- 

 cellular cavity extending up to the protoxylem and involving a few cells of the 

 phloem. The protoxylem cell above is filled with the yellow deposit. 



