have, in growing, produced others, and consequently, the stalks are branched; Ex.: oats, and many grasses, cineraria, &c., woodrush yucca, and agave, meadowsweet, &c.

When the middle branches of a panicle are longer than the rest, it is called a thyrsus; Ex.: lilack, privet, horsechestnut, &c.

A cyme resembles an umbel, in having the flowers level at the top, but the stalks spring from different points of the principal one; Ex.: elder, oleander, &c. There is one variety of the cyme, in which the flowers are produced in the axilla of opposite leaves; and, being crowded, they appear to form a whorl of flowers round the principal stem of the plant: this is one characteristick of a large tribe of plants, of which the mint, thyme, sage, monarda, deadnettle, &c., are well-known examples.

In the vine, the rachis, or principal axis of inflorescence, frequently produces no flower-buds at all, but becomes lengthened, and acquires the property of turning round any neighbouring body, and thus assisting to support the plant.

This false tendril must be carefully distinguished from the true one, which is always a prolongation of the midrib of a leaf; whereas the one in question springs from the axilla of a leaf, and thus indicates its origin.

It is this kind of discrimination between the various forms the different organs of plants assume, that is so important to the advancement and knowledge of botany, and to which the attention of the rational student cannot be too frequently called.

OF BRACTEÆ AND THE INVOLUCRUM.

The leaf, in the axilla of which a flower-bud is produced, is called a bractea, as has been already mentioned.

The most remarkable sort of bractea is that called a spathe, which has been already noticed in describing the species of inflorescence, termed a spadix.

Bracteæ vary greatly in appearance; most usually they are green and herbaceous, like other leaves; but the spathe is coloured, and so are the four bractea which surround the true flower of the hydrangea. Common observers take these for the flower itself, which is small, and escapes observation.

The spathe, or bractea, of many plants is membranous, as the narcissus, the wild garlick, flowing rush, &c.

The outer set of leaves composing a flower-bud are generally alternate, and as the axis grows, they open singly on different parts of it; these are also bracteæ, because other flower-buds are formed in their aille, as has been explained: but when no such secondary buds expand, these bractea appear like small leaves on the principle flower-stalk, as may be seen in the snowthistle, corn-marigold, centaury, oxeye, and many others.

of the wood anemone afford a good example of this

organ.

The head of composite or compound flowers, as they are commonly called, is always surrounded by an involucrum of many leaves, which are imbricated, as has been mentioned; Ex.: dahila, aster, mari gold, &c.

The part of the plant called the artichoke (Cynara scolymus) which is eaten, is the base of the leaves of the involucrum and the receptacle of a flower like a thistle, of the order Compositæ.

Another remarkable form assumed by bracteæ, is the cupule; or the cup of the acorn, the fruit of the oak, &c. In the filbert the cupule preserves the limbs of the separate bracteæ distinct, though these are united at the base: in the beechnut the bracteæ form a tough shell nearly enclosing the fruit: the berry of the yew is a bractea entirely altered in texture, the real fruit being the enclosed seed as it is called.

The inner elementary leaves of the flower-bud are always whorled, or verticillate; and constitute, when expanded, what is commonly called the flower: as soon as these begin to open, the axis, which has hitherto formed the flower-stalk, ceases to grow, and the top of the stalk, or part where these leaves are joined to it, is called the receptacle.

There are rarely less than two, and commonly four whorls or verticils of these inner leaves.

The flower, properly speaking, consists of two or more whorls of elementary leaves, which differ in form and appearance from all others, and are called sexual apparatus, because, by their means, the seed of the plant is formed and matured so as to become capable of growing: these are commonly surrounded by one or more whorls of leaves differing from the inner set, and unlike other leaves, which are called floral envelopes, or perianth, but are not essential to the flower, as will be further explained.

CHYMISTRY.

SILICON.

Although silicon, in combination with oxygen, is one of the most abundant substances in nature, so much so as to entitle it to be considered the basis of the inorganick, as carbon is of the organick creation, it is only very lately that the art of chymistry has succeeded in separating it in small quantities, by difficult and complicated processes.

Silicon has been obtained in the form of a solid, in a disintegrated state, of a dark-brown colour, and without metallick lustre. It does not conduct electricity, and is incombustible either in air or oxygen gas. It may be exposed to the strongest heat without fusing or undergoing any other change. It decomposes water, and becomes converted into oxyde of silicon, or selix, by union with its oxygen. Although much uncertainty still prevails in all experiments When two or more bracteæ, instead of appear-with this difficultly-obtained element, there is reason ing singly on the principal flower-stalk, are opposite or verticillate, they form an involucrum.

There is an involucrum at the point where the stalks of the umbel branch out, in many umbelliferous plants, as in the wild carrot, samphire, waterparsnip, &c. (See figures of umbel.)

The large bractes immediately below the flowers

to suppose that, in the state of oxyde, it is combined with its own weight of oxygen, and that its equivalent is 8.

SILICON AND OXYGEN.

Silex enters into the composition of most earthy minerals, and exists in a state of almost perfect pu

rity, in the form of colourless rock-crystal or crystals of 6 to 16: so that, supposing the acid to be a com of quartz. By heating these substances redhot, and pound of two equivalents of oxygen, the number for throwing them into water, they may be disintegrated boron will be 6, and that for the acid 22. Boracick and reduced to fine powder by pounding. Sufficient- acid may be obtained by dissolving a given weight ly pure silex may also be obtained by calcining com- of a salt called borax (which is imported from India mon flints at a low red heat. They may then be easily in a rough state under the name of tincal) in boiling reduced to powder. In this state they must be mix- water; and adding half its weight of sulphurick acid, ed with four times their weight of carbonate of pot-previously diluted with an equal quantity of water. ash, and fused in a crucible, by a strong red heat. Upon evaporation of the solution and cooling, shiA strong effervescence will take place; after which ning, scaly crystals will be precipitated, which is the heat must be urged till the materials enter into the substance in question. It is also found native in complete and quiet fusion. The compound may be the neighbourhood of volcanoes. dissolved, when cold, in water; and the alkaline solution, after filtration, dropped gradually into diluted sulphurick or muriatick acid. An abundant precipitate will subside, which, after pouring off the liquid which covers it, must be thoroughly washed till the water comes away perfectly tasteless: it must then be dried.

Silex thus obtained is a perfectly white and tasteless powder, which feels harsh between the fingers. Its specifick gravity is 2.6. It is insoluble in water, and is not acted upon by any acid except the fluorick, whose properties will be hereafter described. When first prepared, and minutely divided, it is taken up by solutions of pure potash or soda, but not by the volatile alkali ammonia.

Silex, in combination with the fixed alkalis, forms the basis of that inestimable product of art, glass. When one part of very pure sand is ignited with three of carbonate of potash, a compound is formed, which is very soluble, and deliquesces (attracts moisture) in the air. When these proportions are reversed, and three parts of sand and one of carbonate of potash are fused together, the product is insoluble in water and all the acids except the fluorick, and possesses the well-known properties of glass. Its purity depends upon the purity of the ingredients employed in its manufacture. Green bottle-glass is made of impure materials; such as sand, which contains a con-siderable proportion of iron, and the commonest kind of soda called kelp. Window-glass is made of pure alkali, and sand which is free from iron; and for plate-glass the utmost care is taken to provide both the materials in their purest forms.

BORON.

When equal parts of the metal potassium, and very pure boracick acid, are heated together in a copper tube, at a temperature of about 302° Fahrenheit, they suddenly become redhot: the metal disappears, and, when the product has been washed with warm water, a greenish-brown or olive-coloured substance is obtained, which is boron.

It is destitute of smell, and possesses very little taste. It is sparingly soluble in water, and the solution reddens vegetable blue colours; and what is very singular, it also reddens the yellow colour of turmerick in the manner of alkalis. It is soluble in alcohol, and communicates a beautiful green colour to its flame. It fuses when heated, and gives off its water of crystallization to the amount of about 44 parts in the hundred. It is therefore probable that the crystallized acid is composed of 1 equivalent acid 2 ditto of water

THE FIVE SENSES.

THE SENSE OF SIGHT.-No. V.

DEFENCES OF THE EYE.

22

18

40

The "loving kindness" of the Creator is beautifully exhibited in the provisions he has made for the preservation of life amidst the multifarious dangers which hourly threaten it with extinction. To notice only a few of the more obvious instances, as they float on the surface of his oceanick wisdom, we may hold up to admiration the well-compacted strength, the wind-like fleetness, and the ready sagacity, aliko which combine to give the lion the supremacy, of forests, deserts, and cultivated plains. An impenetrable shell saves the torpid and slow-going tortoise from the crush of the elephant's foot; and, in the hour of need, an armature of spines, like threatening spears, couching in every direction, preserve by intimidation, the weak and unoffending hedgehog from a host of powerful assailants. Upon our heaths the furze-bush stands as a fortress to the gentle linnet against the pursuit of the rapacious hawk; and, in tropick lands, the pendant nests of the loxia and Baltimore birds swing from the end of graceful boughs, like the bunches of sour grapes in the fable, to set on edge the teeth of the wily serpent, who would fain destroy the tender broods, but dares not trust his weight to the fragile branches. In our retired streets, when a family of loquacious sparrows squat down to discuss their roadside morsels, a lonely fellow, chosen from the party, sits high up on the corner of some adjacent spout, as a sentinel, to warn them of a coming stone or an advancing cat; and when Boracick Acid.—There is considerable discrepance the plenitude of summer flowers, and the insects in the results or experiments upon the quantity of oxy- which make each opening bud a nation, are exhaustgen which is absorbed by boron during its combustion; ed ;-when the harvest-fields cease to yield their inbut there is reason to think tha! 100 grains condense crease, and the gray mists of coming winter clothe 266.6 grains of that gas which is in the proportion the autumnal eves with sadness, then millions of the

It is insoluble in water, tasteless, and does not effect the colour of blue vegetables. It may be exposed to the strongest heat in close vessels without undergoing any change: but when heated to about 600° Fahrenheit in the open air, it burns vividly, absorbs oxygen, and is converted into boracick acid. It is a non-conductor of electricity.

BORON AND OXYGEN.

feathered tribes, borne on strong aerial wings, cross | effected by a curtain-like membrane, called the tuni

seas and deserts to seek afar off a warmer sun and ca conjunctiva.

richer lands. Innumerable genera of beetles-" the creeping things of the earth,"-covered with thick plates of shelly armour, return hollow sounds, instead of sweet morsels, to the eager bills of hungry birds. One of these "armed knights," called the bombardier, puffs at his enemies a cloud of poisonous smoke, and walks quietly away in the very face of half-suffocated foes. But to make an end of examples which are infinite in number as they are infinite in wisdom, we shall only notice the cuttle-fish, which in the eyes of ignorance, would appear to be a very helpless creature, but is, in reality, as well defended as a king by loyal subjects. This inhabitant of the waters, the moment he is menaced by any danger, discharges a quantity of intensely black fluid, in the centre of which he rests, and by which he becomes suddenly invisible. This fluid forms the basis of Chinese, or, as it is more commonly called, Indian ink.

The conservative providences of God are, however, no less evidenced in the preservation of particular organs, and little and apparently insignificant parts of animals: thus, the heart is preserved from rupture by the great strength of its twisted fibres, and from external injury by the breast-bone and ribs; the bowels from corrosion by a soft covering of mucus; the teeth from too rapid wear, by their enamel; and the eye from a multitude of distressing evils, by various admirable contrivances, which it will now be our business to describe.

1. THE ORBIT OF THE EYE.

The first defence of the eye consists in its lodgement within the walls of a strong bony chamber, called the orbit. This cavity is composed wholly and in part of seven curvilinear bones, severally called os frontis, os sphenoidale, os ethmoides, os maxillare, os male, os unguis, and os palati.

The edge or rim of the cavity is formed by the os frontis, os maxillare, and os malæ; and the rest of the bones contribute to form the bottom and sides. The bottom is perforated by the foramen opticum, an angular hole, to give passage to the optick and other nerves, blood vessels, &c. The whole chamber is lined by a continuation of the dura mater, a membrane which protects the brain.

The two orbits, in their natural positions, might be compared to two funnels, placed horizontally, side by side, opening with their mouths outwards. In these fastnesses the eyeballs are most effectually preserved from external violence. Concussions are dispersed in the joinings of the bones, which, had the orbit been formed of a single piece, instead of seven, might have often suffered fracture from their influence. The situation of the orbits in contributing to the safety of the eyes is also most "express and admirable;" for, be it observed, they stand centrally between the projections of the nose, brow, and cheek bones, which, in cases of a fall or a blow,

receive the entire shock.

2. THE CURTAINS OF THE EYE.

It is necessary that the interiour of the socket of the eye should be guarded from the intrusion of dust or other extraneous matters. This is ingeniously

Section of the eye, showing its situation in the orbit. This membrane, which is also called the adnata, is an infected prolongation of the skin of the eyelids. Before, however, we proceed to describe it, the reader will please to examine closely the following diagram, by which he will acquire a clearer idea than words can convey of its form and situation, and, consequently, be better able to understand the remarks that follow. Let a represent the eyeball, and b the upper and lower lids. Now it is plainly manifest

that some additional contrivance is wanting to prevent dust or other bodies working their way through passages at cc, between the ball and the lid, into the socket of the eye, where their presence would excite insufferable and incurable pains. To meet this exigency, we find that the common skin of the eyelids d d, after covering their respective edges, goes inwards a little way between the lid and the ball, and then turning backwards, is reflected over the surface of the cornea, where, to prevent the obstruction of vision that would otherwise follow, it becomes perfectly transparent. We think that no part of our marvellous bodies exhibits a more pleasing instance of the economy, wisdom, and tenderness of the Creator. The economy of this arrangement is evidenced in the circumstance of no new organ having been created for the purpose-it is an adaption of the skin of the eyelids. Its wisdom is shown in the simplicity of its design, in the unerring truth

with which its functions are performed, and in the means of a number of little pipes or ducts, which prosingular circumstance that the difficulty of the case ceed from it, and open upon the inner surface of the uphad to be overcome by one of greater magnitude- per eyelid We have already described, at Section that of passing the skin of the eyebrows across the very pupil. But God, whose "understanding is infinite," with a majesty which is heightened rather than diminished by the littleness of the objects, steers the course between pain, on the one hand, and blindness on the other, by making the membrane, where it covers the pupil, "transparent." And the tenderness of his care is shown in the fact, that without this little but difficult contrivance, we could not long have used our eyes; but with it we can live our threescore years and ten without annoyance, even from the smoke and dust of the city.

3. THE EYELIDS.

These are composed of the common integuments,

with a cartilaginous margin to give them shape, and The eyelids separated, and viewed from behind; a, the lachrymai muscular fibres to give them motion. The cartilage gland; 6, the ducts from ditto; c, the mouths of these ducts; d, the which forms the margin of the lids is called the tar-puncta lachrymalia: e, the meibomean glands, described in Section 3. sus, and, like all the parts of the eye, is an exquisite 2. the contrivance by which particles of dust, &c. piece of mechanism. It lies like a hoop on their edges, and, from its stiffness, keeps them of a circular figure, so that they close neatly over the eye, and meet with the most perfect accuracy.

The upper eyelid only is moved for the admission of light to the eye; it is raised, or in common language," the eye is opened," by a muscle called the levator palpebre. In "shutting the eye," the closure of the lids is effected by a muscle called orbicularis palpebrarum, which acts with great power on both eyelids.

are kept from the inner chamber of the eye; but we have now to explain the use of tears in cleansing the surface of the eyeball, from similar impurities. When motes rest upon the eyeball, they are, by "winking," immediately wiped off into the channel of the lower lid, when the exquisite sensibility of the membrane by which it is lined, excites the lachrymal gland to a copious discharge of tear water; the eye is suffused, and the offending atoms floated to the inner angle of the lids, and discharged. But here the remedy threatens to become a disease, and an apImmediately within the edges of the eyelids, be- paratus is wanted for draining off the superfluous neath the surface, a number of beautiful little glands water, which, if it were left, would dazzle the sight, are embedded, called the meibomean glands, and from inflame the lids, and cause the lashes to rot at their these, about twenty or thirty ducts, or pipes, open roots, and fall. This would at once have made upon the edge of each eyelid. In the glands a white man a miserable creature, and therefore God, who, greasy matter is secreted from the blood, and slow- as Paley remarks, has made no organ to irritate or ly poured by the ducts upon the edge of the lids, give pain, but all for pleasure and convenience, has, which they defend from being inflamed by the tears, in this instance, made a beautiful provision for the and assist also in striking them together during defence of the eye in the creation of sleep. It is this matter in a dried state which we pick from the inner corners of the eyes, on arising in the morning.

Upon the outer edge of the eyelids, fringes of hairs called the lashes, defend the eye from insects, and are of constant use in mitigating the "too fierce impression" of the sun's light.

4. THE SECRETION AND DISTRIBUTION OF TEARS.

Tears, which equally express our joys, sorrows, pity, and affections, flow more constantly than we are accustomed to consider. Like spoiled children we may literally be said to be "always crying ;" for, whether asleep or awake, the brilliant tears pursue their crystal course in a perpetual stream over the eyeball, moistening its surface, and washing away its impurities. This, as a defensive provision, is that which we have now chiefly to consider.

5. THE LACHRYMAL GLAND.

6. THE PUNCTA LACHRYMALIA, AND THE LACHRYMAL

SACK AND DUCT.

The eyelids viewed from before; a, the canalicula lachrymates, the lachrymal sack. The puncta lachrymalia are two small holes, placed at the inner angle of the eyelids, forming the mouths of a double canal (canalicula lachrymates) or duct for draining off the tears from the eye into

The lachrymal gland is a small spongy body, of a flattened form, seated in the hollow of the bone in the upper and outer part of the orbit, just beneath the outer end of the brow. Its office is to secrete the nose. the fluid of the tears from the blood, and to discharge

The lachrymal sack is a bag of an oval shape, fixed it over the surface of the eyeball. This it performs by to the end of the double canal, and lies in a depresVOL. III.-42