of the inner surface of the bladders, and consist of four, less often of two, divergent arms or cells. The mode in which they act is not clear; but it is demonstrated that they possess the faculty of absorbing nitrogenous matter, salts of ammonia, or infusion of meat. Bodies of a somewhat similar character were observed by Mr. Darwin in the case of Aldrovanda, where he at one time conjectured that they performed the function of absorbing the indigestible portion of the food. I can scarcely doubt that they are homologous with the bodies described by me as "ganglia" in Drosera, and especially in Pinguicula, the function of which is at present unknown. May they not be rudimentary "quadrifids"?

A very remarkable species of bladderwort, U. montana, a native of tropical South America, is not aquatic, but is said to be epiphytic. The bladders, which are extremely minute, are borne on the underground thread-like rhizomes, and are produced in extraordinary numbers. They are closed by a valve on which are a number of minute glands, and bear internally rows of short, thick, quadrifid processes; and apparently capture and detain a number of minute insects, on which the plant feeds. This is the only species of Utricularia which is not aquatic or a native of marshes. U. nelumbifolia has the very singular habit of growing in the water which collects in the bottom of the leaves of a large Tillandsia, inhabiting an arid rocky part of the Organ Mountains, Brazil, at an elevation of 5,000 ft. above the sea. It propagates itself by runners, which direct themselves towards the nearest plant of Tillandsia.

Polypompholyx is a native of Western Australia, and Genlisea of Brazil. In this last genus some of the leaves are elongated into a very narrow cylinder, half an inch to an inch in length, in the middle of which is a minute swelling or tubercle, in which organic matter is found. The neck of the cylinder is furnished with rows of bristles attached to ridges and pointing downwards, which would effectually prevent the escape of any insect that may descend the neck into the utricle, and with a number of quadrifid cells or processes, very closely resembling those already described in Pinguicula, the function of which can only be conjectured.

The order Nepenthaceæ comprises the single genus Nepenthes, which includes a considerable number of species, mostly natives of the East Indies and Australasia, and well known in hot-houses in this country as "Pitcher-plants." The pitcher consists partly of the leaf-stalk and partly of the blade of the leaf, and contains in its lower portion, to the depth of an inch or more, a fluid which was formerly believed to be nearly pure and potable water; but analysis shows it to contain in solution a considerable proportion of mineral salts. Buried in this fluid is fre

quently found a great mass of dead flies and other insects, which have been apparently lured into the pitcher by the secreted fluid; and, their escape being prevented by a rim furnished with bristles pointing downwards below its mouth, have there miserably perished. It was determined by Dr. Hooker that the fluid is distinctly acid, and that it possesses the power, not merely of hastening the decay, but of actually digesting the bodies of the insects drowned in it. He also made the additional remarkable observation that when removed from the pitcher and placed in a glass vessel, although still acid, it has entirely lost its power of digestion. This singular fact is interpreted by Mr. Darwin-and with great probability-to indicate that the actual agent in the digestion is a ferment of a nature similar to pepsin, which is secreted only during the absorption of some digestible nitrogenous substance. In the walls of the pitchers of Nepenthes are minute bodies resembling and possibly homologous to the "quadrifids," or rudimentary papillæ of Genlisea or Pinguicula.

To the last order, Sarraceniaceæ, belong the three genera Surracenia, Darlingtonia, and Heliamphora, natives of America, also cultivated in this country under the name of "Side-saddle plants." The pitchers in this instance consist of the convoluted stalk of the leaf only, the blade forming the lid. They have not at present been subjected to the same careful examination as Nepenthes; but, from the observations of Dr. Hooker, Dr. Canby, and others, there is little doubt that they will be found to present very similar phenomena.

From the fact that the plants we have now passed under review belong to families very widely separated from one another on any system of classification, it is highly probable that phenomena of a similar character still remain to be discovered in other groups of the vegetable kingdom. Although, as we said at the outset, the assimilation of animal food by plants is no newly discovered fact, it must still be admitted that the series of observations here recorded-and especially the apparent production by vegetables of a digestive ferment performing all the functions of pepsin in the animal economy-form one of the most important and interesting additions to our knowledge of vegetable physiology that have been made for many years.

EXPLANATION OF PLATE CXXVI.

FIG. 1. Drosera rotundifolia; natural size.

FIG. 2. A leaf, × 2.

FIG. 3. A leaf, with imprisoned insect; the tentacles partially inflected,

x 4.

FIG. 4. A leaf, with nearly all the tentacles closely inflected, × 4.

FIG. 5. A tentacle, greatly magnified.

FIG. 6. Internal structure of tentacle, showing spiral vessels.

FIG. 7. Section exposing under surface of epidermis of upper side of leaf; a, stomata; b, "ganglia," or arrested papillæ.

FIG. 8. Pinguicula vulgaris; natural size.

FIG. 9. Portion of upper surface of leaf, with two glands, magnified. FIG. 10. Gland, greatly magnified.

FIG. 11. Section exposing under surface of epidermis of upper side of leaf; a, stomata; b, "ganglia," or arrested papillæ.

FIG. 6 after Warming, the rest from nature.

366

OUR SUBMARINE DEFENCES.

BY CAPTAIN C. ORDE BROWNE, R.A. [RETIRED].

[PLATE_CXXVII.]

N the spring of 1873 our equipments of torpedo warfare were engines, known as submarine mines, and those of a locomotive character to which the word "torpedo" has been more peculiarly applied. During the two years that have since elapsed, some progress has been made in the development of the latter class of destructive engines. Whitehead's fish torpedoes have been manufactured in considerable numbers, and their powers have been increased, especially in the most important matter, that of speed in their "running." In short, both Whitehead's and Harvey's torpedoes have received much attention, and they have been brought to greater perfection. Nevertheless, no change has taken place in either of them of such a character as to call for special notice. This is not the case with the first class of engine mentioned, namely, submarine mines. With these a remarkable series of experiments has been carried out, known as the Oberon experiments, the result of which has been to prove that our whole system of submarine mines must be changed. In fact, at this moment we may look upon ourselves as in a state of transition from one system to another, although the substance of the Committee report is not yet made known.

The Oberon experiments were instituted to ascertain, as exactly as possible, the effect of a submarine mine exploding at various distances from a vessel of the modern type. For this purpose the Oberon was fitted with a bottom and sides resembling those of H.M.S. Hercules, and was "tested to destruction," as the phrase is; that is to say, she was exposed to the action of the class of mine proposed to be adopted generally for our lines of defence, at first at a considerable distance, but gradually brought nearer to the vessel until she should be completely disabled from further action. The experiments were * Vide "Torpedoes,' by A. Hilliard Atteridge. REVIEW," April 1873.

"POPULAR SCIENCE

very complete and well carried out, and it is hardly necessary to add, were very costly.

The

The system of mines which it was then proposed to employ in defence of harbours generally consisted of lines of ground charges of compressed gun-cotton, of 500 lbs. each, the depth of water for which such charges were best suited being about eight fathoms, and this depth is a very common one. charges were to be in galvanic connection with the look-out stations or firing-points, so as to enable them to be fired at the will of an operator; self-acting gear, to explode them on contact with an enemy's ship, being also provided. The object of the experiments was to ascertain the distance at which a vessel would be destroyed by the explosion of a mine, and also the necessary interval between the mines, to secure each one from the effects of explosion of those contiguous to it. It is obvious that a certain relationship must exist between these distances respectively, for while it is imperative that the channel should be completely closed against the entrance of an enemy, it is most desirable that the first explosion should not extend beyond the mine acting on the vessel, because it would open a wide gap in the line of defence. With a single line of mines it would be necessary that the interval which would be sufficient to prevent injury from an adjacent explosion should not, under any circumstances, be more than double the distance at which the destruction of a vessel might be considered certain. As, however, channels are defended by several lines of mines, those forming one line covering the intervals in the line next in front, the conditions become modified to a certain extent. Altogether it was scarcely questioned that an efficient system of defence, with large ground charges of 500 lbs. of cotton, might be organised; and if so, this was for many reasons to be preferred to the alternative system, consisting of numerous small charges floated close to the surface of the water, on which we shall have to say more hereafter.

On August 6 the first experiment took place, at Stokes Bay, under the direction of the Special Committee, of which Sir W. Jervois is president. We give the details of this trial, as obtained from official sources, and published at the time in the "Engineer," the editor of which periodical has kindly placed the information and cuts herewith at our disposal.

The Oberon was in the following condition :-The inlet and outlet valves of her condensers were left open. The Kingston valve of her feed-pipe was closed. The water-line was 2 inches higher than the top of her condenser. The original weight of her hull, before fitting her with special bottom, had been 590 tons; as now fitted, it was 920 tons. Her cables and condensers weighed about 80 tons. Her starboard side had forty