SCIENCE NOTES.

Otago Witness, Issue 3195, 9 June 1915, Page 77

SCIENCE NOTES.

Explosive Darts Against Zeppelins. — Mr R. E. Robertson, of Dublin, has produced an invention designed for the destruction of Zeppelin balloons by aeroplanes. It consists of a steel dart, fitted at its rear with fishhook-like projections. The dart is v holl,ow, and contains an explosive which burns with a fierce, sharp flame. When such a dart is dropped from an aeroplane upon a Zeppelin or other gas balloon, the hooks catch in the fabric after the point of the dart has pierced: it, and the explo sive charge is ignited by the pulling backward of a friction detonator. As the explosion takes place inside the gasbag, its effects are expected to be disastrous. When Ice Prevents Freezing.—

At a recent convention held in Chicago the question arose as to why fruit was frozen in oars containing no ice, while in those containing ice, fruit was not frozen, even when the temperature was much below the free sing-point. _ In the Scientific American Ur John D. Bonnar, of Buffalo, offers the following explanation;—ln the car containing ice the chill of the air is neutralised by the action of the ice when the temperature drops below that of the ice. This results from the release of latent heat as _a result of congealation of vapour contained in the air, while the resultant ice, formed out of the vapour, will precipitate itself upon the ice just as rapidly as it reaches that body of frozen water; ihus when the fresh ice is formed there is likewise a release of the latent heat of the vapour, amounting, at steam heat, to 526dcg. Thus the air oi the car is kept warm by the latent heat given up by tno action of its contained ice upon the vapour carrying such hidden heat This latent heat, thus released, is the warming agent which preserves vegetables and fruits from freezing in cars or refrigerators containing ice. Tno fruit and vegetables, while largely water, yet being in the form of organic compounds, will freeze at a lower temperature than pure water. Medicinal Plants. — There is sure to be a- scarcity of medicinal plants this year—especially those grown on the Continent. Belladonna, henbane, and foxglove are three of the principal plants required. Aconite root, although less used, has hitherto been almost exclusively imported from Germany at a price at which it does not pay to grow the plant in Great Britain. At tno present price, however, il would pay to cultivate it. In the damp, peaty soil of Scotland it would grow exceedingly well, as it is naturally a plant oi .damp, peaty, mountain declivities. Camomile flowers, for our own supply of which wo have hitherto been largely dependent upon Belgium and Franco, grow well in any damp, grassy soil, though, curiously enough, they form double flowers better where there is good drainage. The flowers when open require to be protected from the rain and! gathered on a dry day; but if this can be clone in Belgium, the care and foresight of those people may at least be copied in England. Gunpowder From Trees.—

One of the industries which Belgium and Germany have hitherto kept out of our hands is a supremely important one — namely, the growing of dogwood, which yields the very pure carbon necessary for gunpowder, and the growing of aldcrwood. the charcoal" from which is used for the coarser kinds of .gunpowder. The wood actually used under the name of dogwood is that of Rhamnos frangula deprived of its bark. This small tree grows freely m tire South and Midlands of England on peaty, siliceous soil, and sometimes on slightly calcareous soil, eo . long as it is moist and well drained. It could easily be grown by the Government on the Crown lands of the New Forest in any quantity or on the outskirts of Dartmoor, where it occurs already as a wild plant. On the Continent it is pollarded or coppiced so as to produce long, straight shoots, which are allowed to develop until as thick as the thumb and then cut. There is some demand also for the bark, which is not required for gunpowder-making, so that the growth should bo doubly profitable. Alder is so common a tree by streams and swamps all over England’, and is so hardy and easily grown on waste heath land whereon there is moisture, that it seems inconceivable that the Board of Agriculture at Home should not pay close attention to the possibilities of tlie 'country with regard to the articles which have hitherto been imported from abroad.

Plant Tissues That Beat Like Hearts. —

In certain plants (says a writer in the Scientific American) we observe what are known as spontaneous movements. Desmodium cryrans (or the telegraph plant) of India is a. conspicuous example. The lateral leaflets execute pulsating movements which are not unlike the rhythmic movement oi the heart. Professor Bose has studied this curious phenomenon, and finds that it has more than a superficial resemblance to the boating of cardiac tissue. The records obtained show that the rhythmic tissues of the plant are extraordinarily similar to thess of the animal. By the application of ligature the pulsation of the heart is arrested; a similar arrest occurs in the telegraph plant by the proper application of ligature. Cold lowers the frequency of a frog’s heartbeat; it also lowers the frequency of the telegraph plant’s pulsation. Rise of temperature produces an opposite effect in both the animal heart and in the heating leaflet. Alcohol and dilute carbon dioxide prolong the period, while strong applications arrest pulsation altogether. Dilute vapour of other and carbon disulphide induce a temporary arrest, revival tak’ng place after substitution of fresh air. Copper sulphate and potassium cyanide, both poisons, stop pulsation, potassium the more quickly oi the two. No satisfactory theory has been offered to explain these “ spontmeous ” movements. Professor Bose believes that he has shown that there is no such thing as a spontaneous movement. The energy that makes a heart boat or a leaflet vibrate is derived from external sources directly or from the excess of such energy already accumulated and held latent in the tissue. When the stored supply is exhausted activity ceases, only to be renewed again by fresh stimulation. How Plants Suffocate.— Gases have as marked an effect on plants as on animals. Carbon dioxide is popu-

larly supposed to bo good for plants. Professor Bose shows that it is just as depressing and poisonous to a plant as to an animal. as might be expected after this, is stimulating, so much so that _ a fatigued plant can he refreshed by its means. Alcohol vapour produces first exaltation and then depression, the plant responding in a very human way. Ether likewise depresses, but is not so narcotic as chloroform. Carbon disulphide resembles ether in its effect. Coal gas is moderately depressing. Ammonia abolishes excitability, for as long as two hours if strong vapour is employed. Sulphuretted hydrogen is not only depressing, but extremely poisonous in its effect, and since it is found in largo quantities in city atmospheres, we can now well understand why it is impossible for some plants to thrive in towns at all. Nitrogen dioxide is fatal, and so is->; sulphur dioxide. That plants die like animals we all know; but we do not know the exact moment when they die. For hours a dead plant seems alive. There is no twitch, no death spasm. Dr Bose has succeeded not only in noting the precise moment when a plant gives up its life, but in recording its death spasm. The plant is heated very gradually so as to avoid all excitation. This is clone by placing the plant in a water bath, the temperature of which is continually raised by the application of a gas or spirit flame. At 50dog Centigrade a spasmodic extraction takes place, and attempts to obtain response, after this sharp inversion of the record, fail, oven though the plant ; s cooled down to its normal temperature. This death temperature of 60deg is constant for all plants.