538 Forestry Quarterly. 



In a series of articles in the Comtes Rendus 



Effect on the deleterious action of road tar on 



of neighboring trees and other vegetation 



Tarring Roads several French writers have developed 

 on quite a controversy. While it is generally 



Vegetation. admitted that, at least under certain con- 



ditions, a stunting of shoots and leaves, 

 usually associated with discoloration, is produced, the discussion 

 still wages around the point as to whether it is the dust particles 

 from the tarred roads, or the vapors, which produce the injury. 



Mirande holds to the latter view, and thinks that the vapors 

 released at ordinary temperatures penetrate the leaf cells and kill 

 them by plasmolytic rupture of the plasma membrane, causing a 

 discoloration and often a liberation of certain gases. These 

 phenomena he thinks due to a dififusion, after death, of cell sub- 

 stances which react chemically (most often by diastatic action) 

 to produce new compounds, some of which are freed at the sur- 

 face. With certain leaves, such as cherry laurel, which contain 

 glusosides of hydrocyanic acid, a blackening occurs, together with 

 a liberation of HCN. 



He studied the action of a large number of organic vapors on 

 such leaves, among them being the various tar constituents, other 

 hydrocarbons and derivatives, alcohols, phenols, acids, ethers, 

 aldehydes, ketones, amines, amides', and nitrites, and showed that 

 the discoloration, with or without the evolution of HCN, is pro- 

 duced by a great number of widely different chemical compounds. 

 Fine dust of tar, asphalt, and bitumen gave no appreciable results, 

 even in strong sunlight. From these laboratory experiments he 

 concludes that vapors from tarred roads, when sufficient in 

 amount, as in dry, warm weather, with calm air, especially along 

 narrow roads lined with vegetation, can produce injurious effects, 

 and thinks that tarring should be done with circumspection. 



Griffon investigated the problem from 1908 to 1910 and secured 

 laboratory results similar to Mirande. However, he contends 

 that laboratory data derived from bell- jar experiments cannot be 

 safely applied to field conditions. He bases this opinion on cer- 

 tain of his open air experiments, and states that his personal in- 

 quiry in the suburbs of Paris, southern France and England, 



