40 DISEASES OF CULTIVATED PLANTS 



pounds of sulphur dioxide (or 748 tons) are given off each 

 day. 



Placing sulphur on hot-water pipes is always a risky 

 experiment, and sometimes results in disaster- The above 

 account explains how this is brought about. If the heat is 

 above a certain point some of the sulphur at all events is 

 converted into sulphur dioxide; this in the presence of 

 moisture eventually becomes sulphuric acid. Both these 

 substances are extremely injurious to plants. 



Coal gas. The leakage of gas from faulty pipes often 

 causes considerable injury to plants. The roots of trees are 

 completely dead and rotten before the cause of injury is 

 suspected. In such cases the bark of the trunk becomes 

 dry and frequently falls away in large patches. Mr. Aggett, 

 Superintendent of Public Gardens, Bermondsey, who has 

 had much experience of the injury caused by the leakage 

 of gas in the seventy miles of streets under his supervision,, 

 states that after trees had been killed by gas in the soil, 

 when a space of six feet square of the affected area was 

 cleared and replaced with new soil (after the pipe had been 

 repaired), the young trees perished, and it occurred to him 

 to place a lining of wet clay over the sides and bottom 

 of the hole, and the result proved in every way satisfactory. 

 Unless this precaution is taken, two or three years must 

 elapse before the gas has completely escaped from the soil. 



Creosote fumes. During recent years since wood-paving 

 has been introduced, the fumes from the creosote used for 

 dressing the blocks has proved disastrous to vegetation. 

 Bedding plants of all kinds are promptly blackened, 

 shrivelled, and killed, and the foliage of trees is also 

 destroyed or severely injured. 



Aggett, W. H., 'Trees affected by gas,' The Garden, 60, 

 p. 246 (1906). 



Haselhoff, E., and Lindau, G., Die Beschadigung der 

 Vegetation durch Ranch (1903). 



Haywood, J. K., ' Injury to Vegetation by Smelter Fumes,' 

 U.S. Dep. Agr. Chemistry, Bull. No. 89 (1905). 



Wieler, A., Untersuchungen iiber die Einwirkung schwe- 

 fliger Saure auf die Pflanzen (1905). 



