114 FOREST PROTECTION 



incrustating substances and owing to the presence of more 

 moisture, more starch and more albiunen. 



The insects co-operate with the fungi to an unknown ex- 

 tent. Corky bark being fungus-proof, many spores enter the 

 galleries of boring insects either carried by the wind or car- 

 ried in the "fur" of borers and enemies of borers. It might 

 be stated that the insects distribute spores in the same man- 

 ner in which the birds or the rodents distribute seeds. A par- 

 ticularly interesting case is that of "Ambrosia," a fungus 

 supposed to be raised by the Ambrosia beetles. Cyllene ro- 

 binise makes possible the inroads of Polyporus rimosus. Dis- 

 coloration of the sapwood coincides with the attacks of Den- 

 droctonus frontalis and follows the "steamships" in oak lum- 

 ber. A fungus-lawn is found in the mines of Lymexylon. 



Infection is performed 



(a) most frequently by spores, 



1. in dew or rain (notably — the lower fungi); 



2. by wind (notably — the higher fungi); 



3. by insects (rarely, after Tubeuf); 



4. by forcible ejection of spores from sporocarps, asci 

 and sporangia. 



(b) more rarely by mycelium, 



1. notably when the mycelium lives in the earth, or rather 

 in the roots {Trametes radiciperda, Agaricus melleus "(Rhizo- 

 morphs)"; 



2. also above ground, the mycelium spreading from plant 

 to plant {TrichosphcBria, Herpotrichia). 



Many fimgi appear immediately after the affection of 

 the tree by other detrimental influences (e. g. after insects, 

 fire, storm, drought), so that it is possible to decide upon the 

 immediate cause of damage inflicted only by the test of arti- 

 ficial infection. The fungi found present upon a dead tree 

 can never be considered, eo ipso, as tree killers. 



In many cases the mycelixmi of the tree killer has dis- 

 appeared when the tree is dead; and only sporocarps may be 

 still present. Many parasites on the other hand develop 

 sporocarps only saprophytically on a dead substratum. 



Certain timber fungi stop work at once when the tree is 

 cut, e. g., the yellow rot fungus of black locust and the peck- 

 iness fungus of bald cypress. The progress of decay, in such 

 cases, ends with the death of the tree. 



The speed at which a fungus disease spreads from a given 

 point of attack is entirely unknown. This speed is very fast 

 in the case of saprophytes working in dead sapwood; it is prob- 

 ably very slow in the case of parasitic fungi attacking the 

 heartwood of grown trees. 



