American iron-cased vessels in actual warfare, imperfectly as they are constructed when compared with the Warrior or Black Prince, is very remarkable. Whilst, on the other hand, the terrible effect of shells on the wooden Cumberland, in the battle of Hampton Roads, which, in a short half hour, made her interior look like "a burnt and sacked house" and sent her blazing to her ruin, may teach us that, whether absolute invulnerability is attainable or not, it is a prime necessity of modern warfare, and a guarantee for peace, to provide such security as iron will afford against these new missiles.

A Glossary of Mineralogy. By HENRY WILLIAM BRISTOW, F.G.S. Longman. London. 1862.

M'

INERALOGY is a science that has few votaries in England, but a certain knowledge of it is indispensable to the chemist and geologist; and to these the book lately published by Mr. Bristow will be found extremely useful, if not indispensable, for reference.

Mr. Bristow does not confine himself to a mere alphabetical descriptive list. In a short introduction he notices the various properties of minerals and the modes of determining them. Like other geologists who have to use this science as an adjunct, he leans to a chemical arrangement, quoting the method followed by Professor Warrington Smyth at the Museum of Economic Geology, which in all essential features resembles that adopted by Professor Ansted in his Elementary Course of Geology and Mineralogy. He introduces a very large number of synonyms; and the accounts of the principal minerals are pithy, definite, and comprehensive. Remarkable specimens in the public museums of England are referred to, and localities are not neglected. The composition is quoted either by chemical symbols or as a distinct analysis.

In the present state of mineralogical science-and it is not likely soon to improve there is a great advantage in the alphabetical arrangement, as those who have consulted the works of Dana and even of Phillips, in its most approved form, will generally admit; and we doubt not that Mr. Bristow's book will be useful. We would suggest, however, that in a future edition he should give a few more cross references, and bring down his list of localities to accord with recent discoveries. It is rather puzzling to have to think under what heading sulphur, silver, and copper are to be sought, and not easy to see why gold should be described under its own name and the other minerals we have mentioned as natives. We miss, too, names so common as Kaolin, finding Pe-tun-tse and Kunkur, which are much less defined varieties. We miss also Lederolite (a variety of Chabasite); Marmatite (a variety of Blende), and a few others. These are pointed out rather to show that a careful revision is desirable, than as finding fault with a task which, on the whole, is very well accomplished.

On the various Contrivances by which British and Foreign Orchids are Fertilized by Insects, &c. By CHAS. DARWIN, M.A. (Illustrated.) Murray.

THE

HE perusal of Mr. Darwin's book on "The various Contrivances by which British and Foreign Orchids are fertilized by Insects," might incline the reader to regard it as the result of nothing less than a life devoted exclusively to the subject. Yet of the great discussion concerning the "origin of species," the present work is, in fact, only a single chapter, the details of which have become inconveniently large to be incorporated with the rest of the argument.

The point which the author here seeks to establish is thus stated. "That nature abhors perpetual self-fertilization." "That marriage between near relations is in some way injurious-and that some unknown great good is derived from the union of individuals which have been kept distinct for many generations."

Self-fertilization is a rare event with the Orchids, and the description of the various contrivances by which the pollen of one plant is kept from contact with its own stigma and conveyed to that of another plant of the same species, occupies nearly the whole of the volume.

Orchids, it appears, are favourite plants with honey-loving insects. When the proboscis of a bee or a moth is inserted into the nectary of an orchid, it first comes in contact with a little capsule or pouch, the membrane of which at the slightest touch is ruptured, setting free a liquid and exposing the sticky ends of two club-shaped organs, to the further ends of which the pollen grains are attached. The sticky ends instantly adhere to the proboscis, which, when retracted, carries with it the pollen clubs fastened upon it in a somewhat erect position. Further down the throat of the nectary lies the stigma.

We have then to observe (first), the retired position of the anther chambers, of which there are two, containing the charged ends of the pollen clubs. (Second.) The prominent position of the viscid ends of the pollen-clubs in the throat of the nectary. (Third.) The manner in which the sticky ends of the pollen-clubs are kept moist, till wanted for use, by being immersed in a little pouch of liquid. (Fourth.) The extreme sensitiveness of the lips of this pouch, which open at the slightest touch imaginable. (Fifth.) The rapid setting of the viscid matter, which hardens into a dry cement in a very short time after the sticky ends of the pollen-clubs have touched the proboscis of an insect. (Sixth.) If the attached clubs remained erect, the proboscis at its next insertion into a flower would press the pollen grains into a position similar to that from which they had been taken, namely, into the anther chambers; but no sooner are the clubs fast than their pedicels uniformly begin to curl forward, bringing the pollenized ends of the clubs almost close to the proboscis in a more forward position, so that when the next flower is visited the proboscis pushes the pollenized tips of the clubs past the anther chambers and right upon the stigma of the flower.

In the genus Catasetum the flower has two slender horns, which when

touched by an insect convey the excitement of the touch to the anther chambers, which instantly discharge the adhesive pollen-clubs at the head of the intruder. Thus, and thus alone, at least three species of the genus Catasetum are fertilized.

Mr. Darwin has manifestly spared no labour in collecting facts illustrative of his subject. He gives a list of twenty-three species of Lepidoptera captured with the pollen-clubs of O. pyramidalis attached to their probosces. He has himself made observations on nearly all the British species of orchids, and upon a large number of exotic species, and he arrives at the conclusion that, "throughout the vast Orchidean order-including, according to Lindley, 433 genera, and probably about 6,000 species-the act of fertilization is almost invariably left to insects."

The chapter on the homologies of Orchids is one of the most interesting portions of the book.

At Torquay, Mr. Darwin watched a number of plants of Spiranthes autumnalis, and saw them visited by humble-bees. "The bees always alighted at the bottom of the spike, and, crawling spirally up it, sucked one flower after another." "I believe humble-bees generally act thus when visiting a dense spike of flowers, as it is most convenient for them; in the same manner as a woodpecker always climbs up a tree in search of insects." This seems a most insignificant observation; but see the result. In the early morning, when the bee starts on her rounds, let us suppose that she alighted on the summit of a spike, she would surely extract pollinia (pollen-clubs) from the uppermost and last opened flowers, but when visiting the next succeeding flower, of which the labellum in all probability would not as yet have moved from the column, for this is slowly and very gradually effected, the pollen masses would often be brushed off her proboscis and be wasted. But nature suffers no such waste. The bee goes first to the lowest flower, and crawling spirally up the spike, effects nothing on the first which she visits till she reaches the upper flowers, then she withdraws the pollinia; she soon flies to another plant, and alighting on the lowest and oldest flower, into which there will be a wide passage from the greater reflection of the labellum, the pollinia will strike the protuberant stigma. If the stigma of the lowest flower has already been. fully fertilized, little or no pollen will be left on its dried surface; but on the next succeeding flower, of which the stigma is viscid, large sheets of pollen will be left. Then, as soon as the bee arrives near the summit of the spike, she will again withdraw fresh pollinia, will fly to the lower flowers on another plant, and fertilize them; and thus as she goes her rounds and adds to her store of honey, she will continually fertilize fresh flowers, and perpetuate the race of our autumnal Spiranthes, which will yield honey to future generations of bees.

106

SCIENTIFIC SUMMARY.

QUARTERLY RETROSPECT.

ASTRONOMY.

SMALL telescopic comet was discovered by Schwabe, at Athens, on

Subsequent observations and calculations proved that it passed its perihelion on June 22. It continued all along very faint, and was only visible in good telescopes. Its least distance from the sun was about ninety-five millions of miles-almost identical with the earth's mean distance from the central body. We have not seen. it noticed that the orbit of this comet bears some resemblance to one discovered at Paris, on September 2, 1698. The direction of motion, the inclination to the ecliptic and the longitudes of the perihelion and node agree pretty well, and the least distance from the sun is not very dissimilar. The comet of 1698 is, however, stated to have been as bright as a star of the second or third magnitude.

A second and much brighter comet was discovered on July 18, at midnight, at the Cambridge (United States) Observatory, in the constellation of Camelopardalus. It was independently detected at Florence, on July 24, and, on the following night, at Rome, by Professor Rosa. On the latter day it is described as being round, with a nebulosity of from three to four minutes in diameter and a distinct nucleus. Although almost circular, it was slightly dilated in the direction of the sun. No tail was visible in the comet-seeker, although with the naked eye one was faintly perceptible. On August 3, when first seen by the writer, the comet was plainly visible to unassisted vision, and a slender tail was distinctly seen in the finder of the telescope. The nucleus was bright, and a well-defined fan-light was seen proceeding from one of the sides, which was almost at angles with the tail. On August 19 the comet had become a very conspicuous object in the Northern hemisphere and the tail could be traced with the naked eye for a distance of eight or ten degrees from the head. The luminous sector had, however, disappeared, and an exceedingly bright jet of cometic matter lay in the contrary direction to the tail. At midmight of August 24, the luminous sector again made its appearance, and a faint envelope was suspected as surrounding that part—a bright jet passed across the fantail from the nucleus, lying almost at right angles to the tail, which latter was as slender as on former occasions, and was separated from the head by an almost dark space. On August 25, at