FOREST PROTECTION 145 



leaves and needles sur- 

 charged with SO|. Such 

 surcharge has no detrimen- 

 tal influence on the state of 

 health of the trees (Hasel- 

 hoff and Lindau, p. 46, p. 

 51, p. 55, p. 56). 



(b) AGE: Old needles contain more 



SO i than young needles. 

 (Haselhoff and Lindau, p. 

 67; Schroeder and Reuss, p. 

 128). 



(c) SEASON: Young leaves contain 



more SO 3 than old leaves. 



(d) POSITION: On the same healthy 



tree, the sulphur contents 

 of the leaves vary accord- 

 ing to the position of the 

 leaves, which position might 

 be 



at the base or at the 

 top of the crown, 

 on the inside or on 

 the outside of the 

 crown. 



(e) ELEVATION: On the slope of a 



hill, the sulphur contents in 

 the healthy leaves of the 

 same tree-species exhibit 

 variations depending on the 

 elevation above sea-level 

 (Schroeder and Reuss, p. 

 126). 



The sulphur contents of given leaves and need- 

 les are "unmistakably increased" by 

 the reaction on sulphur fumes in all cases 

 where it can be proven that none of the 

 causes of increase above enumerated has 

 or have brought about such increase. It 

 is advisable, as a consequence, 



(1) to back the chemical analysis of 

 the leaves by the chemical 

 analysis of the soil on which 

 such leaves were produced, 

 so as to prove that an in- 



