PLATE 44 



A. — Cross section of stem of mature plant, showing necrosis of internal phloem 

 together with radial elongation of the cells of the perimedullary zone. Outer phloem 

 is well developed and normal. X 130. 



B. — Enlarged view of a necrotic internal phloem group. Almost all of the cells in 

 a group are filled with a granular precipitate. X 400. 



