CHAPTER XXXII 

 MECHANIC DEVELOPMENT OF PATHOLOGIC TISSUES 



Our study of plant pathology would not be complete without a brief 

 reference to the reactions which influence the genesis of the abnormal 

 tissues of diseased plants. The investigation of these questions is a 

 matter of recent development ever since prominence has been given to 

 the experimental methods of studying plant diseases and abnormalities. 

 Kiister gives considerable prominence to these problems in the second 

 edition of his " Pathologische Pflanzenanatomie" (pages 328-398), 

 where we have the last and most authoritative treatment of the subject. 

 As an important factor he mentions the reaction ability of the living 

 cells, both in normal cell division and with inequalities in cell division, for 

 it is recognized that unequal division of the dividing cells plays an im- 

 portant part in pathologic plant anatomy. The polarity of cells is 

 another important element to be considered by the pathologic anatomist, 

 for if by unequal division, there is produced a change in the polarity of 

 the cells concerned in such division, the tissues which arise from such 

 cells will show a different kind of differentiation. 



Miehe has demonstrated the physiologic polarity of cells by plas- 

 molyzing the cells of a marine species of Cladophora. He found, after 

 the destruction of the continuity of the protoplasm from cell to cell by 

 plasmolysis, and the transference of the plant into a solution of deter- 

 mined concentration, that elongated filaments developed, and that 

 rhizoids developed from the basal pole of each of the cells. The epi- 

 dermal cells of the leaves of linden, Tilia platyphylla, when attacked by 

 Eriophyes tilicB develop long cylindric trichomes from the same pole 

 of each cell. 



The reaction capabilities of the cells of different tissues are both 

 quantitative and qualitative. The cells of the epidermis, parenchyma, 

 sap bundles react differently and this is expressed in the formation of 

 intumescences, callus wound-cork and wound-wood out of them. 

 The change in the reaction of cells is also a noteworthy feature in the 

 study of abnormal plant structure. There is a difference between young 



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