FOREST PATHOLOGY IE" FOREST REGULATION. 29 



actual connection is readily established by either the living mistletoe 

 growing out from the swellings or by the small cuplike remains of 

 the stem bases. The swellings render the affected part of the bole 

 unmerchantable. When they break open into what are termed 

 cankers, infection by fungi very readily takes place and a focus of 

 heart rot forms, very much as in the case of Peridermium elatinum 

 on Abies pectinata where Polyporus Jiartigii and Agaricus adiposus * 

 commonly start from cankers caused by the rust fungus. 



The mistletoe cankers very often are the cause of white-fir stems 

 breaking off in a storm, just as Peridermium cankers affect Abies 

 pectinata. This mistletoe is more generally found in the middle or 

 lower parts of the crown; infection takes place only on the very 

 youngest twigs. 



Another mistletoe (Phoradendron bolleanum (Seeman) Coville) 

 nests high up in the top. It often kills the leader; volunteers spring 

 up, which are frequently killed in their turn. Considered in its rela- 

 tion to the totality of leaf functions, the loss from a killing of the 

 leaders can not be very serious, although it may count in combina- 

 tion with other injurious agencies. The same is true for the host of 

 minor parasites and injuries to which the peripheral growing parts — 

 in contrast to the column of wood— are exposed. 



We have seen that the wood of the living tree itself is generally 

 immune to attack from heartwood-destroying fungi as long as it is 

 protected by bark and sapwood. The few exceptions, it seems, are 

 of no great importance in the case of Abies concolor. Pholiota flam- 

 mans is not uncommonly found in white fir and seems to take the 

 place of Armillaria mellea. The exact damage done is still to be 

 studied. Fomes annosus is not yet reported on white fir to the 

 writer's knowledge. Polyporus schweinitzii is not common on the 

 species. All other fungi causing decay can not enter the living 

 tree except through some opening, as far as is known at present. 



In white fir, as in other coniferous trees, small superficial wounds 

 are readily covered over with resin from the bark ; this natural dressing 

 does not allow fungus spores to germinate or the hyphse to develop 

 after germination. Now, white fir is distinctly poor in resin. Large 

 superficial wounds may therefore prove to be more serious. If the 

 bark is destroyed, the cambium is killed and the sapwood dries out 

 and cracks. Through these cracks air gains access to the interior of 

 the tree and must in some way alter the chemistry and physics of 

 the heartwood. The spores of heartwood-destroying fungi lodge in 

 the cracks and upon germination may find a well-prepared substratum 

 in the heartwood. Fungi, like all plants, make certain specific 

 demands as to the chemical composition, water content, oxygen, 

 etc., of the substratum they live on. Given the proper temperature 



1 Hartig, Robert. Lehrbuch der Pflanzenkrankheiten. Ed. 3, p. 153. Berlin, 1900 



