CLASSIFICATION OF PARASITES AND SAPROPHYTES. 5 



As further examples of fungi, capable, as parasites, of killing 

 living cells, but which pass through more or less of their life 

 as saprophytes, may be taken species whose mycelium inhabits 

 the wood of trees and shrubs. Amongst these are numerous 

 Polyporeae, which find admission only by wounds in the wood. 

 At first these destroy and derive nourishment from the substance 

 of dead parts of the wood, but later they begin to attack the 

 parenchyma of the living wood, and extending outwards kill, 

 as they go, cambium, bast, and rind, till they reach the exterior, 

 and there develop sporophores. As examples we may take 

 those species investigated by R. Hartig of Munich, e.g. Poly- 

 porus fomentarius, P. igniarius, P. Hartigii, P. sulphureus, 

 Stereum, liirsutum, Trametes pini} 



The heart-wood is a part of the tree generally avoided by 

 insects, which would in very short time destroy the sap-wood 

 with its rich starch-content, e.g. Annohiae in oak. Again, the 

 heart-wood resists the influence of certain saprophytic fungi 

 much longer than the sap-wood, hence it is preferred as the 

 timber used for railway sleepers. Although in these eases we 

 might describe the heart-wood as possessing antiseptic properties, 

 yet this would scarcely be accurate, since it is just this very 

 heart-wood which is always first attacked by the wound-parasites 

 of trees, and gives them a hold on the tree as parasites. See 

 also Chap. V. 



Since these dangerous tree-fungi can live wholly as sapro- 

 phytes in the heart-wood, and in the sap-wood partly as such, 

 partly as parasites, they are also able to vegetate further, and 

 to reproduce themselves on felled stems, especially when the 

 necessary moisture is provided. Thus, for example, Agaricus 

 adiposiis, a wound-parasite of the silver fir, produces its yellow 

 sporophores on felled stems and split wood during the whole 

 summer in moist parts of the forest, while in a cellar or other 

 moist chamber the development of sporophores may continue over 

 a year. In fact, I have found that a billet of beech-wood, after 

 being placed under a glass and allowed to lie completely dry, 

 on again being soaked from time to time, continued to produce 

 a crop of toadstools annually for five years. 



Some wound-parasites occur occasionally as typical sapro- 

 phytes on dead wood. Thus Polyporus annosus, perhaps better 



^R. Hartig, Zersetzungserscheinungen des Hohes, 1878, and other works. 



