492 RUMBOLD— PATHOLOGICAL ANATOMY OF 



All the cells of the phloem are capable of change with the ex- 

 ception of the stone cells, the bast-fibers and their accompanying 

 cells containing calcium oxalate crystals. Not only can the cells 

 respond which are in the recently formed rings of phloem, but those 

 in the rings eight and nine years old. From the phloem cells are 

 formed bark cambium, cambium and xylem. 



Summary. 



So far an examination of chestnut trees, injected with chemicals 

 in solution, shows that the reaction in the trunks and branches, as 

 evidenced by abnormal tissues, was alike in kind, but varied in 

 intensity. 



With increased distance from a point of injection the tissues 

 became more normal and the area of disturbance decreased. All 

 stages of reaction could be seen in a tree : death, inhibited growth, 

 stimulated growth and no reaction. 



The regions of response were the phloem, cambium, and xylem. 



The Phloem. — The most remarkable response from a histo- 

 logical standpoint, was that given by the phloem. Xylem cells 

 formed in the midst of the phloem region. This xylem was formed 

 by division of the phloem cells with subsequent lignification of the 

 walls, or by lignification of the phloem cell walls without division. 

 All the cells in the phloem were capable of change, except the stone 

 cells, the bast-fibers and those cells containing calcium oxalate 

 crystals, which accompany the bast-fibers. 



The phloem cells changed into bark cambium, cambium and 

 xylem cells. 



Cork formed prematurely, due to an unusual development of 

 bark cambium in the phloem region. 



TJie Cambium. — The cambium layer often disappeared. Its 

 cells were changed into xylem. 



The Xylem. — The xylem responded by increased formation of 

 thylloses and thickening of cell walls. 



Wound Tissue. — Wound tissue formed which varied from 

 normal to abnormal according to the toxicity of the solution injected. 



Botanical Laboratory, 



University of Pennsylvania, 

 April 17, 1916. 



