ELECTRO-CULTURE
About thirty years ago a Swedish scientist, Professor Lemström,
travelled extensively in the Polar regions, and he was greatly struck
by the development of the Polar vegetation. In spite of the lack of
good soil, heat, and light, he observed that this vegetation came to
maturity quicker than that of regions having much more favourable
climates, and that the colours of the flowers were remarkably fresh and
clear, and their perfumes exceptionally strong. This was a surprising
state of things, and Lemström naturally sought a clue to the mystery.
He knew that peculiar electrical conditions prevailed in these high
latitudes, as was shown by the wonderful displays of the Aurora
Borealis, and he came to the conclusion that the development of the
vegetation was due to small currents of electricity continually passing
backwards and forwards between the atmosphere and the Earth. On his
return to civilization Lemström at once began a series of experiments
to determine the effect of electricity upon the growth of plants,
and he succeeded in proving beyond all doubt that plants grown under
electrical influence flourished more abundantly than those grown in
the ordinary way. Lemström’s experiments have been continued by other
investigators, and striking and conclusive results have been obtained.
The air surrounding the Earth is always charged to some extent with
electricity, which in fine weather is usually positive, but changes to
negative on the approach of wet weather. This electricity is always
leaking away to the earth more or less rapidly, and on its way it
passes through the tissues of the vegetation. An exceedingly slow but
constant discharge therefore is probably taking place in the tissues
of all plants. Experiments appear to indicate that the upper part of a
growing plant is negative, and the lower part positive, and at any rate
it is certain that the leaves of a plant give off negative electricity.
In dull weather this discharge is at its minimum, but under the
influence of bright sunshine it goes on with full vigour. It is not
known exactly how this discharge affects the plant, but apparently it
assists its development in some way, and there is no doubt that when
the discharge is at its maximum the flow of sap is most vigorous.
Possibly the electricity helps the plant to assimilate its food, by
making this more readily soluble.
This being so, a plant requires a regular daily supply of uninterrupted
sunshine in order to arrive at its highest possible state of maturity.
In our notoriously variable climate there are many days with only
short intermittent periods of bright sunshine, and many other days
without any sunshine at all. Now if, on these dull days, we can perform
at least a part of the work of the sunshine, and strengthen to some
extent the minute currents passing through the tissues of a plant, the
development of this plant should be accelerated, and this is found
to be the case. Under electrical influence plants not only arrive at
maturity quicker, but also in most cases their yield is larger and of
finer quality.
Lemström used a large influence machine as the source of electricity
in his experiments in electro-culture. Such machines are very suitable
for experimental work on a small scale, and much valuable work has
been done with them by Professor Priestly and others; but they have
the great drawback of being uncertain in working. They are quite
satisfactory so long as the atmosphere remains dry, but in damp weather
they are often very erratic, and may require hours of patient labour to
coax them to start. For this reason an induction coil is more suitable
for continuous work on an extensive scale.
The most satisfactory apparatus for electro-culture is that used in the
Lodge-Newman method, designed by Sir Oliver Lodge and his son, working
in conjunction with Mr. Newman. This consists of a large induction
coil supplied with current from a dynamo driven by a small engine, or
from the public mains if available. This coil is fitted with a spark
gap, and the high-tension current goes through four or five vacuum
valve globes, the invention of Sir Oliver Lodge, which permit the
current to pass through them in one direction only. This is necessary
because, as we saw in Chapter VIII., two opposite currents are induced
in the secondary winding of the coil, one at the make and the other
at the break of the primary circuit. Although the condenser fitted in
the base of the coil suppresses to a great extent the current induced
on making the circuit, still the current from the coil is not quite
uni-directional, but it is made so by the vacuum rectifying valves.
These are arranged to pass only the positive current, and this current
is led to overhead wires out in the field to be electrified. Lemström
used wires at a height of 18 inches from the ground, but these were
very much in the way, and in the Lodge-Newman system the main wires
are carried on large porcelain insulators fixed at the top of poles
at a height of about 15 feet. This arrangement allows carting and all
other agricultural operations to be carried on as usual. The poles
are set round the field, about one to the acre, and from these main
wires finer ones are carried across the field. These wires are placed
about 30 feet apart, so that the whole field is covered by a network
of wires. The electricity supplied to the wires is at a pressure of
about 100,000 volts, and this is constantly being discharged into
the air above the plants. It then passes through the plants, and
so reaches the earth. This system may be applied also to plants
growing in greenhouses, but owing to the confined space, and to the
amount of metal about, in the shape of hot-water pipes and wires for
supporting plants such as vines and cucumbers, it is difficult to make
satisfactory arrangements to produce the discharge.
The results obtained with this apparatus at Evesham, in
Gloucestershire, by Mr. Newman, have been most striking. With
wheat, increases of from 20 per cent. to nearly 40 per cent. have
been obtained, and the electrified wheat is of better quality
than unelectrified wheat grown at the same place, and, apart from
electrification, under exactly the same conditions. In some instances
the electrified wheat was as much as 8 inches higher than the
unelectrified wheat. Mr. Newman believes that by electrification land
yielding normally from 30 to 40 bushels of wheat per acre can be made
to yield 50 or even 60 bushels per acre. With cucumbers under glass
increases of 17 per cent. have been obtained, and in the case of
strawberries, increases of 36 per cent. with old plants, and 80 per
cent. with one-year-old plants. In almost every case electrification
has produced a marked increase in the crop, and in the few cases
where there has been a decrease the crops were ready earlier than the
normal. For instance, in one experiment with broad beans a decrease
of 15 per cent. resulted, but the beans were ready for picking five
days earlier. In another case a decrease of 11½ per cent. occurred
with strawberries, but the fruit was ready for picking some days
before the unelectrified fruit, and also was much sweeter. In some of
the experiments resulting in a decrease in the yield it is probable
that the electrification was overdone, so that the plants were
over-stimulated. It seems likely that the best results will be obtained
only by adjusting the intensity and the duration of the electrification
in accordance with the atmospheric conditions, and also with the nature
of the crop, for there is no doubt that plants vary considerably in
their electrical requirements. A great deal more experiment is required
however to enable this to be done with anything like certainty.
Unlike the farmer, the market gardener has to produce one crop after
another throughout the year. To make up for the absence of sufficient
sunshine he has to resort to “forcing” in many cases, but unfortunately
this process, besides being costly, generally results in the production
of a crop of inferior quality. Evidently the work of the market
gardener would be greatly facilitated by some artificial substitute
for sunshine, to keep his plants growing properly in dull weather. In
1880, Sir William Siemens, knowing that the composition of the light
of the electric arc was closely similar to that of sunlight, commenced
experiments with an arc lamp in a large greenhouse. His idea was to add
to the effects of the solar light by using the arc lamp throughout the
night. His first efforts were unsuccessful, and he discovered that this
was due to the use of the naked light, which apparently contained rays
too powerful for the plants. He then passed the light through glass,
which filtered out the more powerful rays, and this arrangement was
most successful, the plants responding readily to the artificial light.
More scientifically planned experiments were carried out at the London
Royal Botanic Gardens in 1907, by Mr. B. H. Thwaite, and these showed
that by using the arc lamp for about five hours every night, a great
difference between the treated plants and other similar plants grown
normally could be produced in less than a month. Other experiments made
in the United States with the arc lamp, and also with ordinary electric
incandescent lamps, gave similar results, and it was noticed that the
improvement was specially marked with cress, lettuce, spinach, and
other plants of this nature.
In 1910, Miss E. C. Dudgeon, of Dumfries, commenced a series of
experiments with the Cooper-Hewitt mercury vapour lamp. Two greenhouses
were employed, one of which was fitted with this lamp. Seeds of various
plants were sown in small pots, one pot of each kind being placed in
each house. The temperature and other conditions were kept as nearly
alike as possible in both houses, and in the experimental house the
lamp was kept going for about five hours every night. In every case the
seeds in the experimental house germinated several days before those
in the other house, and the resulting plants were healthy and robust.
Later experiments carried out by Miss Dudgeon with plants were equally
successful.
From these experiments it appears that the electric arc, and still
more the mercury vapour lamp, are likely to prove of great value to
the market gardener. As compared with the arc lamp, the mercury vapour
lamp has the great advantage of requiring scarcely any attention, and
also it uses less current. Unlike the products of ordinary forcing by
heat, the plants grown under the influence of the mercury vapour light
are quite sturdy, so that they can be planted out with scarcely any
“hardening off.” The crop yields too are larger, and of better quality.
The wonderful effects produced by the Cooper-Hewitt lamp are certainly
not due to heat, for this lamp emits few heat rays. The results may
be due partly to longer hours worked by the plants, but this does
not explain the greater accumulation of chlorophyll and stronger
development of fibre.
Most of us are familiar with the yarn about the poultry keeper who
fitted all his nests with trap-doors, so that when a hen laid an
egg, the trap-door opened under the weight and allowed the egg to
fall through into a box lined with hay. The hen then looked round,
and finding no egg, at once set to work to lay another. This in turn
dropped, another egg was laid, and so on. It is slightly doubtful
whether the modern hen could be swindled in this bare-faced manner, but
it is certain that she can be deluded into working overtime. The scheme
is absurdly simple. Electric lamps are fitted in the fowl-house, and at
sunset the light is switched on. The unsuspecting hens, who are just
thinking about retiring for the night, come to the conclusion that the
day is not yet over, and so they continue to lay. This is not a yarn,
but solid fact, and the increase in the egg yield obtained in this way
by different poultry keepers ranges from 10 per cent. upwards. Indeed,
one poultry expert claims to have obtained an increase of about 40 per
cent.
The ease with which a uniform temperature can be maintained by electric
heating has been utilized in incubator hatching of chickens. By means
of a specially designed electric radiator the incubator is kept at the
right temperature throughout the hatching period. When the chickens
emerge from the eggs they are transferred to another contrivance
called a “brooder,” which also is electrically heated, the heat being
decreased gradually day by day until the chicks are sturdy enough to
do without it. Even at this stage however the chickens do not always
escape from the clutches of electricity. Some rearers have adopted the
electric light swindle for the youngsters, switching on the light
after the chickens have had a fair amount of slumber, so that they
start feeding again. In this way the chickens are persuaded to consume
more food in the twenty-four hours, and the resulting gain in weight
is said to be considerable. More interesting than this scheme is the
method of rearing chickens under the influence of an electric discharge
from wires supplied with high-tension current. Comparative tests show
that electrified chickens have a smaller mortality and a much greater
rate of growth than chickens brought up in the ordinary way. It even is
said that the electrified chickens have more kindly dispositions than
their unelectrified relatives!
Possibly the high-tension discharge may turn out to be as beneficial
to animals as it has been proved to be for plants, but so far there is
little reliable evidence on this point, owing to lack of experimenters.
A test carried out in the United States with a flock of sheep is worth
mention. The flock was divided into two parts, one-half being placed
in a field under ordinary conditions, and the other in a field having
a system of overhead discharge wires, similar to those used in the
Lodge-Newman system. The final result was that the electrified sheep
produced more than twice as many lambs as the unelectrified sheep, and
also a much greater weight of wool. If further experiments confirm this
result, the British farmer will do well to consider the advisability of
electrifying his live-stock.