719 



only 1-50,000 of its volume in sulfurous acid. Schroder states^ that one 

 one-millionth will prove injurious if allowed to act for some time. Such 

 slight amounts are certainly present in many kinds of smoke, formed by the 

 oxidation of hard coal, which contains sulfur. Moreover, since sulfur in 

 the form of iron sulfid is an abundant element in hard coal, it may be 

 assumed that, as Morren says, we establish a poison centre for plants with 

 every chimney we erect. 



Yet, at any rate, we should not carry this anxiety too far. The experi- 

 ments, proving the injuriousness of such small amounts of gas, were made 

 in a space enclosed by a bell jar and the gas usually acted for several hours. 



This corresponds in everyday life only to the constitution of the air 

 in the immediate proximity of an industrial establishment, such as smelt- 

 ing house, coke oven, etc., in a narrow valley where the smoke lies day 

 and night in great masses above the vegetation. In the majority of cases 

 the motion of the air, and especially wind, together with the character- 

 istic oxidation of sulfurous acid into sulfuric acid when in contact with 

 moisture, serve as a protection against the most extreme action of the 

 poison, and against immediate death. In any case, however, it would be 

 well, in regions where hard coal or peat- is burned, to choose for industries 

 producing a great deal of smoke, such positions as are removed as far as 

 possible from large plantations, especially from tracts of trees. 



The gaseous products, from burning hard coal free from sulfur are not 

 injurious to vegetation''. If the coal, however, contains some sulfur and gives 

 it off into the air as sulfurous acid, it will be taken up by the leaf-organs 

 of the conifers and deciduous trees. According to v. .Schroder the greater 

 part is retained in these organs and only a small amount is carried into the 

 wood of the plant. The experiments made by Freitag'* directly in this con- 

 nection indicate that we shall have to consider the leaves as the main organs 

 for taking up the poison. Yet all leaves do not take up equal amounts of 

 the poison offered them; in this, conifers differ markedly from deciduous 

 trees. Under similar external conditions, with equally large leaf surfaces, 

 the former take up less sulfurous acid than do the' latter. Yet it can not 

 be said that a plant suffers more when it has taken up a greater amount of 

 gas. The power of resistance depends rather upon the special organization 

 of the plant. In this connection, the supposition is pertinent that the 

 anatomy, especially the number of stomata, may be determinative for the 

 sensitiveness of a plant. This supposition, however, which has been repeat- 

 edly expressed by Morren, has proved to be erroneous, since Schroder has 



1 Schroder, .J. v., und Reuss, C. Die Beschadigung der Vegetation durcli Raucli 

 usw. Berlin 1883, P. Parey. 



2 According to Stockhardt the smoke from lignite and peat is also injurious, for 

 this fuel contains sulfate of silica. The smoke of lime kilns is less injurious because 

 the lime retains the sulfurous acid form, j"ust as in brick ovens the magnesia content 

 frequently present in the clay acts favorably because of the retention of the sulfurous 

 acid. Chemischer Ackersmann 1872, Part II, p. Ill ff. 



3 Proved for plum and pear trees. 



4 Mitteilung der landwirtsch. Akad. Poppelsdorf. Vol. II, 1S69, p. 34 cit. bei 

 Schroder loc. cit., p. 321. 



