SOME EFFECTS OF FUEL OIL ON PLANTS
GEORG E D. FULLER AND MARGARET R. LEADBEATER
Some years ago a storage tank of fuel oil emptied upon the soil is supposed to have caused the death of several oak trees in a suburb of Chicago.
This caused the writers to make certain preliminary experiments on the
action of such oil on certain potted plants.
While attention had been directed towards the entrance of such oils into
the leaves of plants when applied as a spray (see among others GINSBERG
(2), KNIGHT et al. (4), KELLEY (3), DE ONG (1), and ROHERBAUGH (5)), no
investigation regarding their effects upon roots is known to the writers.
The fuel oil used was purchased from the Consumers Petroleum Company, Chicago, Illinois. It is described commercially as 3236 Baume gravity
gas oil, consisting principally of saturated hydrocarbons. It is obtained in
the refining of petroleum as one of the heavier fractions of distillation. The
viscosity is about 55 seconds Saybolt. In appearance it is medium thin, of a
greenish amber color, and is similar to the "medium oils" which spray investigators have found most useful.
The experiments were carried on with four plants: the tomato, Lycopersicrnt esculentum; the peach, Prunus persica; the apple, Pyrus malus;
and Ageratumn houstonianum. The four were chosen for their availability
rather than for any scientific reason, but they proved suitable material for
the investigation because none of them contained natural oil in sufficient
quantities to interfere with the recognition of the introduced oil in the plant
body, and they gave an interesting variety of reactions. As the most extensive experiments were with tomatoes and peaches, the reactions of these two
species only are being reported.
The tomatoes were from greenhouse stock, all from the same planting,
carbohydrate high and tending to reproduction. The peaches and apples
were year-old seedlings obtained through the courtesy of Dr. M. J. DORSEY,
Chief in Pomology at the University of Illinois. They were planted in good
potting loam, the tomatoes being in 5-inch pots and the peaches in 6-inch.
Two lots of 12 plants each were used for each species divided into sets of
two pots each. One of these sets, without oil, served as the control; the other
five sets had one application of oil applied to the surface of the soil in
amounts of 1, 2, 3, 4, and 5 per cent. by volume of the soil content of the
respective pots. In one lot of each species the soil was heaped about the
stems of the plant so that there was no surface contact of the oil with the
stems. This was designated as the M series; the others constituted the S
series. All plants were watered regularly to maintain proper moisture conditions for good growth and the plants were kept under observation for 51
days.
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PLANT PHYSIOLOGY
Results with tomatoes
The control plants and part of those in soil with 1 per cent. of oil appeared quite healthy and vigorous at the end of the period. The plants of
the M series usually showed injury a day or two before those of the S series.
The first signs of injury were the wilting of the youngest two or three
leaves of the main axis and those of the lateral axes. The whole tip sometimes wilted with the young leaves. Leaf wilting occurred with or without
discoloration. In case of discoloration, the leaves turned either olive-green
or yellow. No oil was found in leaves which had turned olive although it
looked from the outside as if it might be present. Flowers developed if the
buds were fairly mature when injury became apparent, otherwise they
blighted.
Yellowing of the older leaves was not taken as a symptom because the
plants stood rather close together and the checks dropped their oldest leaves
also. However, as the injury advanced all the leaves of the plants yellowed,
wilted, and died. Sometimes the stem collapsed near the surface of the
ground or halfway up the stem, sometimes it remained upright. This seemed
to be a matter of individual resistance for there was no correlation between
doses of oil and methods of degeneration. Wilting occurred in from eight to
fourteen days for the larger doses and twelve to twenty for the smaller
ones. There was less difference in the time of death of the two groups. It
occurred in twenty-two to twenty-eight days in the plants in soil with 4 to 5
per cent. of oil, in twenty-four to forty-two days for those with 3 per cent.
or less, and half the plants in soil with 2 per cent. of oil were still alive
at the end of the experiment.
Sections were made with the use of the freezing microtome from plants
of both the M and S series grown in soil with 1, 3, and 5 per cent. of oil.
These sections were taken from the tips of the plants, from the mid-stems,
from the stems at the surface of the soil, and from the roots. They were
stained with Sudan III and examined for the presence of oil, which was
found in varying amounts in all the plants, with larger amounts in plants
from soil with highest oil content.
The oil was found most regularly in the xylem, particularly the primary,
where the stain brought out small drops clinging to the sides of the vessels
or completely clogging them. Only where it was plentiful did it spread to
the xylem parenchyma or to the rays, being confined to the bundles except
when present in excess. It was next most prominent in the intercellular
spaces of the pith and cortex. In the root, it was about equally distributed
between xylem and cortex, but it was often difficult to tell about the location
because degeneration had proceeded so far that the structures were but ill
defined. Judging by color and texture, the roots were certainly badly injured by the oil, although they did not always show great quantities of it
within them. Roots of check or low-quantity treatment plants were cream
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FULLER AND LEADBEATER: EFFECTS OF FUEL OIL ON PLANTS
819
to light tan in color, firm, and brittle. Those severely affected by higher percentages were dark red-brown to black, withered, and limp.
Results with peaches
Almost a month elapsed before the peaches showed any response to the
oil treatment. A very small plant (M 5 per cent.) was wilted when visited
on the twenty-fifth day. Very soon afterwards all but one of those at 2 per
cent. and above followed suit. There was no discoloration. The leaves
wilted and died, green. There was no outstanding difference in time between the 2 and the 5 per cent. plants nor between M and S plants. Five
of the eight M trees showed injury at thirty-seven days, four of these dying
after forty days. There were also five S trees injured thirty-seven days
after treatment, taking forty-three to forty-five days to die. All plants in
soil with 2 per cent. of oil or more were dead in forty-five days.
When sections of all representatives of the series were examined, they
were uniform in giving a positive stain for oil only in the cuticle. This fact
remained a puzzle until the root systems were exposed in discarding the
plants. One per cent. of oil seemed below the critical amount, and the
plants which grew in soil with this dosage were alive at the end of the experimental period, and had almost as good root development as the check.
But somewhere between 1 and 2 per cent. the lethal concentration is reached.
From 2 per cent. upward the tops were somewhat stunted, and the roots had
practically disappeared. Only a few limp, brown, straggling ends of the
branches were visible. The control plants showed that their roots had
elongated and had branched freely during the time of the experiment. In
contrast with these the plants in soil with 2 per cent. or more of oil showed
no root growth, but a depletion and decay of the original root system. The
direct damage by the oil seemed, in the peaches, to be confined entirely to the
underground parts but with equally fatal effects.
Discussion
The species examined exhibited marked variation in their reaction to the
oil treatment. Where oil actually entered the tissues a slow death followed.
This was probably a toxic action since no sections seemed to show oil in
enough cells seriously to impede ordinary translocation. Where oil had
apparently not gained entrance to the plant, as in the peaches, some other
factor must have been responsible. Either there was local toxic action at
the roots, or the spread of oil about them was sufficiently complete to prevent
translocation of water in the soil and its absorption by the roots, and the
plant literally died of drought.
It is not known what relation the oil bears to the soil. A small quantity is evidently held among the soil particles by capillarity, since it is only
where larger amounts are added that the oil seemed to move through the
soil. It has been shown that as roots take in water from soil adjacent to
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PLANT PHYSIOLOGY
them, free water will move in from more remote areas to replenish the supply. This would continue if necessary until only the hygroscopic water
remained. Where 3 per cent. or more of oil was added to a pot it was
found concentrated about the roots, which would indicate that a similar
situation obtained with it.
If some definite part is held by the soil particles it would explain the
failure of the lowest quantity to produce results. In the case of tomatoes
and peaches the soil seemed able to take up about 1 per cent. of oil by volume
without injuring them; but when the amount was greater, the effect was
detrimental to the plants.
This investigation opens up many questions particularly of physiological
interest which must be left for future studies. Probably abnormalities
in temperature, humidity, water content, and nutritive relations would have
special meaning when plants are subjected to a test of this sort. It will be
valuable to correlate results of outside experiments with the greenhouse data.
Summary
1. Commercial fuel oil has a harmful effect on plants when brought into
contact with their roots, through the soil.
2. The effect becomes fatal when the quantity is raised above the critical
point for a species.
3. The effect may or may not be due to penetration.
4. If the oil has penetrated the tissues, it is most commonly found in the
primary xylem; to a lesser extent it enters the secondary xylem, and the
intercellular spaces of the pith and cortex.
5. Contact does not seem to be a primary cause of death.
UNIVERSITY OF CHICAGO
CHICAGO, ILLINOIS
1.
2.
3.
4.
5.
LITERATURE CITED
DE ONG, E. R. Present trends in oil sprays. Jour. Econ. Entom. 24:
978-985. 1931.
GINSBERG, J. M. Penetration of oils into plant tissue. Jour. Agr. Res.
43: 452-474. 1930.
KELLEY, V. M. Effect of certain hydrocarbon oils on respiration of
foliage and dormant twigs of apple. Illinois Agr. Exp. Sta. Bull.
348. 37-406. 1930.
KNIGaT, H. A., CHAMBERLIN, J. C., and SAMUELS, C. D. Some limiting
factors in the use of saturated petroleum oils as insecticides. Plant
Physiol. 4: 299-321. 1929.
ROHRBAUGH, P. W. Penetration and accumulation of petroleum spray
oils in the leaves, twigs, and fruit of citrus trees. Plant Physiol. 9:
699-730. 1934.
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