g(54 JOURNAIv 01- FORESTRY 



acidity of sap not only controls the darkening in extreme cases but is 

 also closely related to the tint of the heartwood of "Sugi" in general, 

 its derivation is quite obscure so far as our knowledge is concerned. 

 A few data will be given for information only. 



Among many trees of "Sugi" in certain stands in the district of 

 Yoshino, only one remained as "red tree" in spite of the fact that it 

 had been wounded. The soil about the tree was acid. One stand in 

 the same district, very famous for the production of high quality 

 "red wood" for many reproductions, had a conspicuous acid soil as 

 compared with the other twenty stands. 



As the wounds are responsible for the precocious formation of 

 heartwood and at the same time induces its darkening, "black tree" 

 may occur earlier than normal "red tree." The trees once trans- 

 formed to "black tree" can scarcely return to "red tree" in the course 

 of many years. The darkening taking place on exposure to air after 

 felling and sawing can not be seen, however, in the "black trees" 

 which are over about 150 years old. The staining in such cases is not 

 so deep colored as the darkening in the younger trees ; it is generally 

 light, suggesting the gradual fading of the original darkening.- 



VAI,UE OE "bEACK wood" TO THE TRADE AND SOME PRACTICAI, 

 PRECAUTIONS 



Owing to its supposed durability, "black wood" is preferred for 

 telephone poles, bridge and ship building, etc. But "black wood" is 

 generally considered of inferior quality for the many other uses, to 

 which it may be put. It is, therefore, of economic importance to 

 prevent the production of "black wood." The only practical method 

 is, of course, of a purely preventive nature. In stands where "black 

 trees" are apt to be produced, care must be taken in the pruning of 

 living branches to avoid wounds of a size effective for the production 

 of "black tree." 



So called "seasoning in stands" that is leaving one part of the crown 

 after the felling and peeling of trees, the method prevailing in 

 Yoshino and other districts, is recommendable for such trees of "black 

 tree" as first stain on exposure to air, to avoid the extreme darkening. 

 But it is a fallacy that some darkening substance is removed to the 

 twigs by this means or that this method is effective in inducing "black 

 wood" to turn to "red wood," as believed among the people in the 

 above districts. We found that no coloring substance and especially 



