The liJdcL- Zones Fonncd h/j Wood-Dedroging Fungi 17 



tlio protection wood tlicory, is of more iinportauce. Liiidrotli 

 investigated the jDathologic heartwood (the protection wood 

 of Frank) fonnd in a thin zone surrounding portions of wood 

 decomposed by Polyporus nigricans Fries. Such pathologic 

 heartwood pro'ved to be rich in infiltration products and 

 thereby increased in weight, hardness, and durability. 

 lie stated that this infiltrating substance arises through the 

 eoanbined action of the fungus in the rotten heartwood, and 

 the oxygen of the air. The pathologic heartwood was consid- 

 ered by him to retard the progress of the fungal decom- 

 position. 



To sum up these rather di^'ersified results of the earlier 

 workers, the brown substajice commonly occurring in the 

 vicinity of wounds in wood is to Ije considered as a secretion 

 of the parenchyma cells. This substance is said to have the 

 function, either in conjunction with the tyloses or in their 

 absence, of occluding the severed vessels. By this means the 

 air in the tissues is rendered independent of the atmospheric 

 jiressure. In this manner the tissues are protected against 

 the entrance of fungi and consequent decay. The cells are 

 stimulated to form tyloses and decomposition products by 

 means of fungal hyphae, wound stimulus, entrance of oxygen, 

 and pressure changes. The discolored wood is denoted, ac- 

 cording to its position in the stem, as protection wood, false 

 (pathologic) heart, or protection heart (when surrounding 

 wounded areas). It is said to be similar to normal hcart- 

 \^•ood. 



Miincli (1910-) arrived at somewhat different results by 

 which he very clearly settled tlie differences of opinion exist- 

 ing among the earlier authors. His results concern, first of 

 all, the origin of the brown sulrstance, the decomposition 

 products, arising in the protection wood. He states that this 

 substance is not a secretion of living cells but that it arises 

 only after the death of the cells as an oxidation product of 

 the cell contents. 



