Tlic Blade Zones Formed hij W cod-Destroying Fungi 23 



pureum. In these he found, in the vicinity of the hjphae 

 growing nearest the vessels, that the protoplasm of the paren- 

 chyma cells was dead or nearly so. It had contracted from 

 the cell walls and gave slight or no further plasmolysis with 

 suitable reagents. The remaining cell contents had collected 

 as colorless drops which were soon broA\Tied and mixed with 

 the dead protoplasm so that the pith rays en masse appeared 

 browm. Even here the brown substance gave all the reactions 

 recorded for wound gnm except that the resistance against 

 the use of cold hydrochloric acid and potassium chlorate was 

 many times greater than that given by Frank. Miinch was 

 convinced that even in this case — of death through fungi — • 

 the brown substance arises only after the death of the cells 

 but never, however, in living tissues. He observed this 

 clearly by microscopic examination of infected living twigs 

 and pieces of wood, especially in those cases in which he per- 

 mitted fungal hyphae to grow over the surface of living wood 

 in a moist chamber. In this case he could easily follow the 

 advance of the fungus and the broA\Tiing. It was evident to 

 him that the latter does not precede the fungous attack but 

 appears only at some distance behind the growing, pointed 

 hyphae where the sound wood cells had been killed by the 

 fungus.^ He concluded that the browning therefore can not 

 be a preventive measure, a means of protection of the plant 

 against fungous attack. 



According to Miinch (1910^) the substances which furnish 

 the decomposition products may leave the cells, after the 

 death of the protoplasm, and exude into the lumina of the 

 vessels. For this, however, a greater quantity of cell sap is 

 required than is at the disposal of the dr)dng poplar twigs. 

 He believes that the oxidation of these products occurs mostly 

 in the vessels which are rich in oxygen. The oxidation of 



'According to Miinch it is different in living trees where the fungal 

 ferments become distributed by the sap-flow and can then act injuriously 

 upon distant-lying cells. 



