S46 JOURNAI. OF FORESTRY 



come to the author's notice. We owe to Dr. v. Tubeuf and F. W. 

 Neger the most extensive investigations in this field where fungi do 

 not come into play. But it is clear that v. Tubeuf s conclusions ^ are 

 not applicable at all points to this case. Very significant in relation to 

 this discoloration process are Neger's studies of basswood, where a 

 similar phenomenon has been observed.^ Yet it may be pointed out that 

 his chemical data do not satisfactorily support his conclusions. It 

 is significant that the same auth9r in his next work did not state posi- 

 tively that the red staining undergone by the wood of alder was 

 caused by the co-existence of tannin and iron.* Thus the chemical 

 hypothesis as to the cause of the production of "black tree" has no 

 evidence in its favor and our data prove that there is no reason to be- 

 lieve that tannin and ferrous compounds, or either one of them sep- 

 arately, is responsible for the appearance of "black tree." 



2. "Site" had often been suggested by careful foresters as the in- 

 direct cause of the phemonenon, as in the case of "black oak." ^ There 

 is evidence that site is responsible, to some extent at least, for the 

 production of "black tree." as will be shown in this article. It can- 

 not, however, be the only cause as trees growing closely together may 

 be partly normal trees and partly "black trees." On the other hand, 

 there is every reason to believe that site includes a number of influ- 

 ences, of which some may come into play as indirect causes rather 

 than as direct ones. The nature of such factors is. however, unknown. 

 It is evident, therefore, that this hypothesis cannot be accepted as con- 

 clusive beyond the suggestion that site would play on the whole a sub- 

 ordinate role. 



3. The third hypothesis, namely that "black trees" are a variety ol 

 "Sugi" is a very commonly accepted view at present in some districts, 

 "black trees" are to some extent externally dififerent from normal 

 individuals ; which would favor this hypothesis but most of these 

 diflferences are of local significance only. Furthermore, these external 

 differences recognized as the characteristics of "black tree" are not 

 present before the age at which the heart wood begins to exhibit the 

 darkening characteristic of "black wood." In this connection it is 

 interesting to consider those cases where the "black wood" occurs 



*v. Tubeuf, C. Tintenholz in lebenden Fichten. Naturw. Zeits. f. Forst- u 

 Landw., Juni, 1911, pp. 273-276. 



' Neger, F. W. Die Vergriinung des f rischen Lindenholzes, id, Juni, 1910, pp. 

 305-313. 



* Neger, F. W. Die Rotung des frischen Erlenholzes, id. 1911, pp. 96-105. 



* Keen, G. R. Aeroplane Timber. London, 1919. 



