158 
PARK AND 
CEMETERY. 
which are likely to affect a tree. It requires, however, pretty 
close observation and thorough understanding of conditions 
in order to distinguish gas poisoning from some other types 
of injury which are sometimes likely to arise. For example, 
in the Gypsy Moth district about Boston, the trunks of many 
trees have been treated with crude oil and various other sub- 
stances which are exceedingly injurious to trees. Crude oil 
or kerosene, when sprayed on the bark of a tree, will pene- 
trate the bark and kill the cambium, and these substances 
will also penetrate the wood to some extent. Unless one is 
perfectly familiar with the characteristics of trees poisoned 
with gas, it would be a very easy matter to confound these 
two classes of injuries. In both cases the bark becomes 
loose and falls off the tree very quickly. From careful 
observations of the trunks of trees, however, the effects of 
crude oil can be generally distinguished from those caused by 
gas by one who is familiar with these characteristic injuries. 
Trees affected with illuminating gas are very susceptible to 
rapid disintegration (see illustration). One of the first effects 
of gas poisoning in summer would be a yellowing and dry- 
ing up of the foliage and a more or less loss of the same, 
according to the degree of poisoning. The trunk of the tree 
generally presents a darkened color, showing an absence of 
life, but this feature is not always present. The occurrence 
of various kinds of fungi on trees affected by gas is rather 
conspicuous, since these fungi make their appearance very 
quickly after a tree has been injured from gas, whereas 
on trees dying from other causes it is sometimes many years 
before the bark becomes covered with fungi. The wood of 
trees injured by gas is sometimes discolored, especially the 
sap wood, and it has peculiar, characteristic odors which 
constitute a good diagnostic feature. Sometimes, however, 
especially when the tree is injured by gas in late summer, at 
which time the flow of sap is not so pronounced as in the 
spring, the odors of the wood are not so marked. 
The writer has had many years experience in examining 
trees injured by illuminating gas, and has had occasion to 
study many of them each year. In our diagnosis of gas trees 
we make use of a small hatchet which we employ to cut into 
the trunk of a tree for the purpose of examining the tissue. 
In most cases it is only necessary to insert the hatchet into 
the trunk and gradually pull the tissue back to see whether 
it is normal or abnormal. In such cases little injury is done 
to the tree, as a slit will heal over in a short time. In other 
cases it is necessary to take out a chip, and examine the 
tissues under a microscope. An examination of the larger 
roots which extend above the surface of the soil by means 
of a hatchet causes less disfigurement, and the source of 
leakage, if such is present, may be indicated. The escape of 
gas in the soil from a leak 
follows the line of - least re- 
sistance. For this reason, if 
leakage occurs in the street in 
front of a house, one can usu- 
ally detect the odor of gas in 
the cellar, as the gas will fol- 
low the exterior of the pipe 
leading into the cellar. 
There is considerable differ- 
ence in the resistance of soils 
to gas. In gravelly soils we 
have known gas to travel 2,000 
feet without any difficulty and 
escape in the cellar of a house, 
whereas in heavier soils 
gas is more likely to be 
restricted to certain areas. 
The poisonous properties of gas to trees undoubtedly con- 
sist in the coal tar products, which contain such compounds 
as sulphates and cyanides, etc. Gas escaping in the 
soil probably condenses fully as rapidly as in the pipe. The 
gas-drip which is taken out of a pipe is the con- 
densed portion, and this in itself is very rank in odor and 
extremely injurious to plants, whether the volatile products 
are taken in through the leaves or the liquid through the 
roots. It is apparently these condensed products which are 
taken up by the roots and poison the tree. About one or 
two per cent of gas is absorbed by water and the water in 
the soil becomes charged to a certain extent with gas. In 
the course of time, where the leakage is more or less exten- 
sive, the odor of the soil becomes extremely obnoxious. 
This odor disappears very quickly when the soil is aerated; 
in fact, when a gas leak is found, it is an excellent idea to 
leave the ditch open for a few days to get rid of the strong 
odors which are present in the soil. There is a certain adap- 
tability of plants to poisons, and such occurs in the case of 
gas. This probably occurs to some extent in the case of 
trees, but the adaptability is limited, and where the leakage 
of gas is continuous the roots are sure to be poisoned in time. 
The writer has treated various small trees and plants with 
gas, and has grown them in water charged with gas. Gas, 
like many other poisons, acts as a stimulus to a plant at first, 
but eventually it kills the roots. It is possible, however, to 
keep roots alive in water charged with gas every 24 hours 
for a considerable length of time. Finally, however, after 
the plant has absorbed a certain amount of gas, the cambium 
layer is affected, and disintegration takes place rapidly. It 
requires a considerable amount of gas to kill a large tree, 
but it must be borne in mind that the conditions surrounding 
a tree are favorable for maintaining gas in the soil for a long 
time. We once treated a large maple tree with 1,000 cubic 
feet of gas. This was done by digging a hole in the ground 
under the feeding roots to a depth of four feet or more and 
the gas was allowed to escape into the soil at this point for 
a number of months. The result was that not the slightest 
injury was done to the tree. If, however, the same amount 
of gas had been allowed to escape near a tree located near a 
macadamized road and the leakage had extended over a 
period of two years instead of three or four months, some 
injury would have been distinguished.. 
Many gas companies now recognize the fact that a certain 
amount of leakage occurs continually and that a certain num- 
ber of trees are likely to be killed each year; therefore 
they endeavor to settle all damages arising from gas to trees 
out of the courts. In Massachusetts the court has decided in 
more than one instance that a good-sized, well-developed 
