14 BULLETIN 275, U. S. DEPARTMENT OF AGRICULTURE. 



during the last few years. In reason, all figures relating to loss in 

 timber from decay, insects, lightning, etc., should apply only to such 

 forested areas as are accessible at present or which will be in all 

 probability accessible in the not too remote future. Inaccessible 

 stands, whatever their protective value, do not represent timber 

 values, and it is obviously wrong to include them in any estimate 

 of the damage done to our timber stock on hand. 



The rate of progress of decay in the individual tree is altogether 

 unknown beyond vague guesses. 



Hartig 1 has tried to figure the rate of growth of the mycelium, for 

 instance, of Fomes igniarius. Moller 2 has made an attempt to figure 

 the rate of growth of Trametes pini and resulting decay in Pinus 

 silvestris from actual measirrements in artificially infected trees. It 

 is clear that unless such experiments are carried over a great many 

 years, only the rate of growth of juvenile fungus plants starting from 

 the infection can be measured, which can not be taken directly as a 

 guide for figuring the growth of the older or mature fungus plants. 

 Besides, the experiment is based upon the assumption that the 

 fungus, after once having gained access to the interior of the tree, is 

 independent of possible individual differences of its substratum, or, 

 in other words, that the rate of growth is a fixed factor, irrespective 

 of individual properties of the heartwood. This assumption has no 

 solid basis. The rate of growth of the fungus plant, and therewith 

 of decay, is undoubtedly one of the most inaccessible chapters of 

 forest pathology, on account of the difficulty in finding a stable point 

 of issue. There is at present no reliable method known of deter- 

 mining the actual extent of decay in the standing living tree. In- 

 direct methods are the only means presenting themselves to-day; 

 they leave much to be desired with regard to accuracy and can not 

 be expected to yield results unless carried on over a long period. 



What we do know is that decay in standing living timber from 

 heartwood-destroying fungi causes very heavy losses and that decay 

 is progressive. Sporophores develop on decaying trees, and the dis- 

 ease spreads through spores from one tree to other individuals of the 

 same and sometimes of other species. Moreover, the decay starting 

 from an incipient infection progresses in the heartwood of the in- 

 dividual tree until its most valuable lumber is destroyed. Decay 

 being progressive, the cumulative risk from this source in long 

 cutting cycles is therefore far greater than in the case of lightning or 

 other injurious agents. 



Unlike insects, heartwood-destroying fungi have few or no natural 

 enemies; there is no such thing as "biological control" of decay. , 



1 Hartig, Robert. Die Zersetzangserscheinungen des Holzes der Xadelholzbaurne and der Eiche ... p. 116. 

 Berlin, 1S78. 



2 Moller, A. Der Karnpf gegen den Kiefernbaurnsckwamm. Iti Ztschr. Forst- u. Jagdw., Jahrg. 42, 

 1910, Beft 3, pp. 129-146. (See p. 145.) 



