coal, which affords ammonia under some circumstances, should, under others, yield the elements of that alkali in a detached states and the reason why azote is for the most part not to be found in the gas which is first evolved, is, that at a low temperature, that element unites with hydrogen, and composes ammonia. But when the contents of the retort, which for some time have been kept comparatively cool by the escape of condensible fluids, become more intensely heated, ammonia is either not formed, or, if formed, is decomposed again into azotic and hydrogen gases, both of which may be traced in the aeriform products of the advanced stages of distillation. As a matter of practice, it is certainly desirable that the azote existing in coal should enter into the composition of a condensible fluid, rather than that it should escape in a gaseous state; for it is an impurity which, when once mingled with the combustible gas, cannot be removed by any known method, and must materially, impair its illuminating power. That such an effect mustresult from its presence, may be inferred from the experiments of Sir H. Davy, who found that an explosive inixture of carburetted hydrogen and common air was deprived of its combustibility by being mixed with one sixth of its bulk of azotic gas. ›

TO BE CONCLUDED IN OUR NEXT.

On the Aphis Lanigera, or American Blight; with an Account of various Experiments, for the Destruction of the Insect on Apple Trees.

By Sir OSWALD MOSELEY, Bart, M. P. F. H. S. &c.

From the TRANSACTIONS of the LONDON
HORTICULTURAL SOCIETY.

AMONGST the insects which derive their sustenance from the vegetable world, there are none, perhaps, more

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prejudicial than the Aphides; scarcely a plant sexists; which is entirely exempt from their ravages, or which is not infested by a species peculiar to itself. Whilst the singularity of their habits deserves the strict observation of the entomologist, the depredations they so widely commit demand the most accurate attention of the hor ticulturist. In selecting one species out of this exten sive genus, as the subject of the present enquiry, I have been urged by a consideration of the alarming encroach+ ments it is annually making on the luxuries, I may even say on the necessities, of mankind; and although the few observations I am about to make can tend but little to arrest its destructive progress, they may, at leasty in stigate others, better qualified than myself for such an undertaking, to investigate and discover the means of effecting that desirable purpose.

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I have designated this species by the term Lanigera, or wool-bearing, which has been previously applied to it by Sir Joseph Banks, in the second volume of the Hurticultural Transactions, page 162, because I could not find one more appropriate; but, at the same time, I must pre-> mise that the characteristic which gives rise to it is not confined to this species alone. In its formation, it differs from the generality of these insects, by not possessing a horn, or process, on each side of the abdomen: the body is surrounded by bands nearly parallel to each other, commencing at the thorax, and terminating at the extremity of the abdomen. The colour of the full-grown insects approaches to that of lead, and of the youngest to that of amber; the antennæ, or feelers, are proportionably shorter, and the size of the body much smaller, than any other species of this genus; indeed, we might justly that insects so minute could effect mischief so extensive, if we were unacquainted with their amazing fecundity, and the means which they adopt to .

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procure their food. For the latter purpose, nature has furnished them with a proboscis, or snout, which, when they are not feeding, is extended in a horizontal position along the belly, and between the legs; it is armed at the end with a very fine and sting-like point, which they have the power of projecting or withdrawing at pleasure; with this instrument they pierce the sap vessels of the tree, and suck out the juices from thence through the proboscis. They do not frequent the leaves and tender shoots of the trees, as other species of the Aphides do, but they inflict a more deadly wound, by extracting the sap as it circulates beneath the bark. Their snouts are not sufficiently strong to effect this purpose, by penetrating the outer bark, except at the knots and joints, where it is the thinnest; but they generally insinuate themselves into the wounded parts of the tree, where the rough edge of the outer bark shelters them from the inclemency of the weather, as well as from the discerning eye of the gardener; here they pierce, in security, the inner bark, and make rapid progress in their work of destruction. Whenever an apple-tree, however, is attacked by these insects, their secret operations are soon visible in the cankered appearance of the bark, the sickly aspect and scarcity of the leaves, and the almost total want of blossom. Upon a closer inspection, their haunts are easily discovered, by the mealy web in which they are enveloped. This web, when observed through a microscope, resembles an accumulation of the finest cotton threads; it appears to be produced not only from the abdomen, but from each division of the bands which surround their bodies; intermixed with it are an infinite. number of small transparent globules, consisting of a viscid saccharine fluid, the voided excrement of these singular insects. In several other species this excrementitious deposition is the cause of the phenomenon

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known by the name of Honey Dew; but in this, the quantity of saccharine fluid produced is comparatively trifling, or at least, from its local detention in the mealy web, we do not observe it displayed so evidently upon the surface of the surrounding leaves; sometimes, however, large pieces of the web, intermixed with it, fall down, and after a short period produce a similar effect on the subjacent grass.

Whether this species derives its origin from a foreign climate, or whether it may be descended from an indigenous stock, having changed its habits by a change of food, I have neither the opportunity nor the inclination to discuss. It is sufficient for us to know, that the depredations it has committed in our orchards have been confined to the period of a few years; but that even in those few years its increase has been so rapid, and the injury it has caused, in many cases, so fatal, as to call forth the most anxious enquiries after some mode of destroying it, and rescuing our apple-trees from its baneful attacks. To effect this desirable purpose has been the object of different experiments which I have tried, during the two last summers, on several trees. I directed one to be washed with a strong infusion of sulphur in soap-suds, which was forcibly thrown upon the insects from a garden engine; a temporary stupor seemed to affect them, in consequence, but no greater than I had previously observed a violent shower of rain to produce upon them. I applied a strong decoction of tobacco leaves, in a similar method, to another tree, but with no better success. In hot-houses, I had frequently seen the destructive effects of the smoke of tobacco upon insects, but I found considerable difficulty in applying it to trees in the open air, so as to keep it sufficiently compressed to answer the purpose. Having ignited the dried leaves of tobacco in an empty flower-pot, and applied a pair

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of bellows to the hole at the bottom of it, my gardener bound the mouth of the pot to the bough of the appletree with a wet napkin, which prevented the fumes from escaping, whilst the operation of the bellows directed them to the parts affected. The success of this experi ment was much more complete than that which had attended the others; great numbers of the insects perished, but some few, to my great surprise, survived, even after the most careful application of it. Upon the whole, we did not think that the advantages gained were commensurate with the trouble of the operation, and we determined to resort to some more effectual and less tedious process.

When the smallest quantity of oil was dropped from the point of a pin upon a single Aphis, I perceived that it caused instant death; this encouraged me to repeat the experiment on a larger scale. With a painter's brush, we applied train oil to those parts of the tree which were infested by the Aphides, and the result of such application exceeded our most sanguine expectations. It not only effected their destruction at the moment, but we had the satisfaction of observing that every place which we had besmeared with oil, during the last summer, had been cautiously avoided by the insects, during the preSent, although they were still visible on other parts of the same tree. The only doubt which suggested itself to my mind, was, whether the oil might not be injurious to the tree; but the very reverse appeared to be the fact: for wherever the tree had been deprived of its bark, this application had preserved the albumen from the effects of the weather, and the young bark was gradually closing over the wounds. Perhaps, had the whole of the outer bark of the tree been smeared with the oil, it might have proved injurious, by obstructing the pores, and preventing them from imbibing moisture from the atmosphere

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