266 JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. t September is, isso. 
this galvanic influence, had assumed quite a different appearance, 
and soon acquired a healthy luxuriance. Doubts being expressed 
whether it were possible that such apparently insignificant means 
could have alone been the cause of the mischief, and nothing 
short of ocular evidence being convincing, the wooden laths were 
removed, and the case full of healthy Ferns was thus again sub¬ 
jected to the galvanic action as it had been originally. On the 
following morning, or after about twenty-four hours, the plants 
were dull and drooping, mildew had appeared, and the case 
looked unnaturally moist. The next twenty-four hours, however, 
brought matters to a crisis. Fronds were decaying and had 
become covered with fungoid growths, festooning from one to 
another like cobwebs ; whilst the whole interior, both plants and 
soil, emitted most powerfully the peculiar Mushroom odour, and 
in addition to which various minute fungi had sprung up in the 
vegetable remains constituting the soil below. This evidence 
having been accepted as sufficiently conclusive, the laths were 
replaced so as to destroy the galvanic action and render the case 
innocuous as before. On examining it some few hours after¬ 
wards the change that had taken place created no little astonish¬ 
ment. Hardly a trace of the former cobwebby appearance was 
to be seen ; all the fungi had been dried up and had disappeared, 
and the atmosphere within had become clear and dry. 
It is now evident that galvanised wire, having an external 
surface of zinc, when fastened with iron nails must inevitably be 
equally galvanic in its effects, yet when the fastenings are gal¬ 
vanised too the whole is rendered perfectly innocuous like the 
insulated plant case. It is only when dissimilar metals are in 
contact with each other that the wire becomes hurtful. But in 
order to establish more fully the identity of these phenomena 
with electricity, a small battery w r as so arranged that the two 
separate conditions should be going on simultaneously. A portion 
of Cress seed was spread thinly on a piece of thick wet flannel 
placed on a piece of glass, and the two terminal wires from the 
battery w r ere made to rest upon it some little distance apart, so 
that the communication of one with the other was left to be com¬ 
pleted by the moisture; consequently these wires represented re¬ 
spectively the zinc and the iron, and were anticipated to produce 
the same corresponding results, as they unquestionably did. The 
first signs of growth took place amongst those seeds surrounding 
the wire representing the zinc or positive end. They, however, 
made very little progress, but soon died and became blackened, 
and ultimately tenanted by the mycelium of a fungus. At the 
opposite or negative end the seeds were longer in germinating, 
but they became greatly swollen and retained their full bright¬ 
ness, ultimately acquiring a healthy and luxuriant growth, which 
they maintained so long as the action was kept up. 
These very significant features demonstrate the highly impor¬ 
tant fact that under one condition of electricity plants are 
killed but fungi flourish, whilst under the opposite condition 
fnngi are destroyed and plants luxuriate. As, however, the direct 
application of electricity on a useful scale is quite beyond the 
limit of practicability, it is hence very fortunate that electrical 
attraction and chemical affinity are similar. We are enabled to 
accomplish the same ends by having recourse to chemical appli¬ 
ances. Liebig in one of his writings states that “ we know 
nothing whatever of the chemical changes taking place at the 
surface of the earth,” which was unquestionably true at that 
time, but happily does not apply to the present time. The pre¬ 
ceding facts, in conjunction with others belonging to the same 
class, serve to elucidate these proceedings in the most unmistake- 
able manner. One of the first lessons derivable from these views 
is that manures may be separated into two opposite divisions— 
one corresponding with the zinc, and the other with the iron, as 
above. The distinctive feature of these divisions is that one sup¬ 
plies oxygenated food to the plants, while the other is wholly 
devoid of oxygen, and leads to the production of mildew and 
other fungi. Ammonia consists of only hydrogen and nitrogen 
without a particle of oxygen save in the water in which it is 
dissolved, hence it cannot possibly afford any oxygenated nourish¬ 
ment to the plants through its roots, and therefore we must look 
for some other direction for its effects. On the other hand, all 
those substances which redden blue litmus paper owe this pro¬ 
perty to the presence of oxygen, and these have been found by 
experiment to be readily absorbed by roots, whilst ammoniacal 
solutions in their alkaline state are rejected. These results have 
been verified practically on a very fairly extensive scale. An old 
vinery, 30 feet long and containing eight Vines, had become so 
infested with mildew as to be worse than useless, and the opinion 
of one of the oldest and most successful Grape-growers of the 
district was that the only chance of rectification would be by 
cutting down and regrafting. Coupled with this the head 
gardener suggested that unless the border were to be dug-up and 
remade he thought the other would be of little or no use. The 
advice of neither, however, was accepted. The circumstance was 
deemed too valuable in connection with these means to be lost. 
Having witnessed under what conditions mildew originated and 
how it was exterminated by an opposite treatment, this was carried 
out on the same principle, and the result was, that in the follow¬ 
ing season a very fair crop of Grapes was obtained, which coloured 
most satisfactorily, whilst not a trace of mildew was to be found 
in the whole house. Now this mildewed condition had been 
brought about by the excessive use of stale night soil, the am¬ 
monia of which had done the mischief ; therefore, as a test trial, 
one of the end Vines was liberally supplied with a solution of 
guano, and on the following morning spots of mildew were trace¬ 
able all over that Vine, leaving no doubt as to its origin. Tea 
and other Hoses have been treated with equal success, and there¬ 
fore there is reason to hope that this pest may soon become a 
thing of the past. 
In the above-recorded experiment with Cress seed it was ob¬ 
served that those seeds around the positive or oxygen-attracting 
end of the battery were not only killed, but their husks were 
blackened like a piece of half-burnt wood. The like of this may 
be witnessed in almost every garden. Stems and branches of 
trees and plants trained in contact with rusty iron, such as stakes 
and trellises, or fastened with iron hooks or nails to walls or fences, 
are killed precisely in the same manner. Hence, although oxygen 
is so essential to the roots of plants, it is destructive to their 
leaves and stems. These experiments teach us the true use and 
action of oxygen in life, and prove it to be very different from 
what has hitherto been suspected ; but as it forms one of the 
chief agents in growth it is of too much importance to be dragged 
in at the end of a chapter, and therefore (with the Editors’ per¬ 
mission) it will be better that it should be treated more fully in a 
separate communication. — W. K. Bridgman, Norwich. 
CHAPTERS ON INSECTS FOR GARDENERS.—No. 11. 
NEW SERIES. 
When considering in a methodical manner the well-nigh innu¬ 
merable host of species that are placed in the class Insects, we 
may go either from the higher to the lower types, or from the 
lower to the higher. Having pursued in these articles the latter 
plan, and started with the humble wingless insects, such as the 
Fig. 54.—Larva of Tiger Beetle and its tunnel. 
fleas, of the order Aptera, we now reach, in conclusion, the order 
Coleoptera, which is by general agreement of naturalists regarded 
as the highest in structure amongst the orders. Beautiful in 
colour and marking as are many of the butterflies and moths, 
several circumstances, especially their possession of a sucking 
mouth instead of jaws for biting, put them below the rank of the 
beetles and other insects less attractive in appearance than the 
gilded flies that disport in the sunbeams, or the less showy yet 
often richly-tinted moths that haunt the evening shades. Another 
thing that is notable about the order of the beetles is that it 
surpasses all the rest in the vast array of distinct species that 
have already been recognised or suspected. Probably at least 
fifty thousand are contained in collections, and every year is 
adding more as travellers penetrate new regions. Even these 
small islands of ours present us with about three thousand species ; 
only a few of these, however, it is pleasant to know, do injury to 
our fields or gardens, though these species are at times both 
numerous and active. 
It is only necessary to mention some of the beetles that are 
noticeable on cultivated ground to show how great is the variety 
of size and form observable amongst the Coleoptera. We may 
name as illustrations of the order such species as the cockchafer, 
the Bose beetle ; the skipjack, the larvas of which is the wireworm, 
