216 MASS. EXPERIMENT STATION BULLETIN 170. 



Elm trees often show a white streak on the bark, caused by some injury 

 resulting in bleeding, and maples are also quite often affected, sometimes 

 going into a slow decline, followed by death from bleeding alone. These 



injuries are a difficult class to treat, and at present 



no satisfactory method is known. 



Injurious Chemical SuBSTA^x'E. 

 Kerosene Oil. 

 Many different oils have been used for spraying 

 insect pests, some of which have proved reliable and 

 others injurious. Kerosene oil can be used on some 

 plants under certain conditions without causing 

 injury, wliile in other cases it will kill them. A 

 few years ago there was placed on the market a 

 spraying device for the mechanical mixing of kero- 

 sene and water in different proportions, but when 

 these materials are mixed mechanically they separate 

 on the tree, and they have been responsible for the 

 death of many trees. The oil soaks into the bark and 

 often reaches the cambium and sapwood, destroying 

 the tissue ; and we have seen quite a few shade trees 

 killed by spraying with kerosene and water to exter- 

 minate woolly aphis. In some cases every part of 

 the tree touched by the kerosene was injured, while 

 in others the injury was only local, a more com- 

 monly noticed condition on thick bark trees, while 

 the former case was invariably restricted to trees 

 with thin bark. The bark of trees killed by the use 

 of kerosene presents a different appearance and 

 develops usually a different type of fungous flora 

 from the bark of trees dying from other causes; 

 besides, traces of the oil, which remain on the tree 

 for a long time, can be detected by the sense of 

 smell. A fair diagnosis of this type of injury may 

 be made from specimens of the bark, but when there 

 are comparatively slight local injuries it is best to 

 examine the tree in situ. Even slight traces of oil 

 may be detected by removing small portions of 



the outer bark on the sunny side of the tree, the sun's heat causing 



a slight volatilization and perceptible odor. 



Fig 90. —Bleeding 

 elm. The white 

 streak on the limb 

 and trunk shows 

 the slime-flux. 



Gas Oil. 

 Gas oil, a heavy oil used in the manufacture of water gas, is very in- 

 jurious to trees when used as a spray. A few years ago several hundred 

 shade trees were severely injured in one of our eastern cities by spraying 



