PATHOLOGIC PLANT ANATOMY 



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cutting under water, the other extending into moist air. The bark 

 cells were enlarged greatly, producing ball-Hke or weakly lobed forms. 

 Only single cells in the bud hypertrophied and they grew out into large 

 colorless vesicles. Miehe has found Tradescantia virginica a suitable 

 object to produce callous hypertrophies experimentally. The destruc- 

 tion of cells, or cell groups, of the epidermis causes the formation of 

 empty places which are filled by the neighboring cells which close the 



Fig. 146. — Pitted vessel of black locust, 

 Robinia pseudacacia, filled with enlarged 

 parenchyma cells or tyloses. At a the con- 

 nection between tyloses and original cell is 

 seen. (Kiister, Pathologische Pflanzenanal- 

 omie, 1903: 100. 



Fig. 147. — Cross-section through 

 old wood of Mespilodaphne sassafras. 

 The lower vessels contain .stone 

 tyloses, the upper besides stone 

 tyloses, contain thin-walled tyloses. 

 {After Molisch in Kiister, Pathologische 

 Pflanzenanatomie, 1903: 100.) 



opening. Haberlandt in his culture of isolated tissue elements obtained 

 abnormally large cells which should be classed among callous hyper- 

 trophies. He kept alive isolated mesophyll cells from the leaves of the 

 purple dead nettle, Lamiuni purpureiim, for weeks in Knop's solution, 

 or in nutrient sugars, and these cells grew perceptibly at the same time 

 that a thickening of their membranes took place. The exact causative 

 influence in the development of callous hypertrophies is still an open 

 question. 

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