attention to a factor which is of decisive importance in niakinj; tests as to the 

 estimate of injuries due to acid viz., to the very dift'erent amounts of sulfur 

 and chiorin in shade leaves as contrasted with sun leaves. He found in the 

 beech in one square meter of leaf substances: — 



in sun leaves in shade leaves 



SO, 0.2730 g. 0.3004 g. 



CI 0.0190 g. 0.0347 g. 



Therefore, the less abundant the i)roduction of organic substances is 

 the relatively higher becomes the content of sulfuric acid and chiorin. The 

 statements of Wislicenus express the same: "A poorer soil quality, that is, 

 soil constitution of less value physically and chemically, soils specifically 

 unsuitable for the plant genus or primarily insufficient, excessive, or abnor- 

 mally varying water content of the soil create a predisposition to disease 

 from smoke ; among them the chief factor is the lack of water." 



The fact that the conditions in a forest become different because of the 

 falling of the needles and the dying of the branches, indeed, that the appear- 

 ance of deciduous trees is changed, that the trunks become almost entirely 

 free from lichens^ and that the bark of the trunks of beeches takes on a 

 peculiar grey tone, may be mentioned only in passing. The statements of 

 V. Schroder and Reuss point directly to the change in soil constitution. 

 They still say that an accumulation of undecayed needles is formed under 

 spruces chronically injured by smoke and a complete absence of all living 

 vegetation is noticeable as far as the dropping from the tree extends. This 

 indicates a "poisoning of the soil." This is proved by Reuss' experiments, 

 in which he carried soil from a smoke filled region into a zone free from 

 smoke and set out i)lants in it. After three years, the loss in i to 2-year-old 

 seedlings of the ash amounted to 100 per cent., of the maple 92 per cent., 

 of the beech y2 per cent., of the spruce and pine 8 per cent., and of the 

 oak, none. 



Wieler- has now taken in hand especially the (|Uestion of soil poisoning 

 and has proved that under certain circumstances in smoky regions with a 

 continued out-pouring of smoke, sulfurous acid could be proved to a de[)th 

 of 30 cm. and had, therefore, not been changed into sulfuric acid. The 

 latter will also remain uninjurious only so long as it can combine with 

 bases. If these bases are used up in neutralization and are washed away by 

 rain the humic acid present finds no possibility of combination. In fact, all 

 the soil tests made by Wider, from regions injured by smoke, showed great 

 amounts of humic acid. Calcium, which could have combined with the 

 humic acid produced is, therefore, not present in these soils. The other 

 bases, however, with which the humic acid forms soluble compounds (mag- 

 nesium and iron) must have disappeared from the soil. Thereby, naturally, 

 the absorptive power of the soil becomes poorer for other mineral nutritive 

 substances. This refers also to the alkali forming soluble compounds of 



1 Lindau, loc. cit., p. 120. 



- Wieler, Neuere Untersuchungen, etc., p. 314. 



