The odour of flowers has its origin in the volatile oils, elabora by the corolla; its production results from causes both external a internal, but, in both cases, equally beyond our observation. Te perature renders the odour of flowers more or less sensible; if heat is powerful, it dissipates the volatile oils more rapidly than th are renewed: if the heat is very feeble, the volatile oils remain c centrated in the little cells where they were elaborated; under the circumstances the flowers appear to possess but little odour. I if the heat is neither too great nor too little, the volatile oils exh without being dissipated, forming a perfumed atmosphere arou the flowers.

You perceive the reason, that when you walk in a flower gard in the morning or evening, the flowers seem more fragrant than the middle of the day. The air being more charged with humidi is another cause of an increase of fragrance at those times ;( as t moisture, by penetrating the delicate tissue of the corollas, exp the volatile oils. There are some exceptions to the laws just state for some flowers are only odorous during the night, and othe during the day. Some flowers exhale fetid odours, which attra such insects as are usually nourished by putrid animal substanc Many flowers exhale sweet odours; but, however odours may diff in the sensations which they produce, it is certain, that power ones have a stupifying, narcotic effect upon the nerves, and that is dangerous to respire, for any great length of time, even the mo agreeable of them, in a concentrated state.

One important office of the corolla, is to secure those delicate a important organs which it encloses, the stamens and pistils, fro all external injury, and to favour their development. After t germ is fertilized by the influence of the pollen, the corolla fad away, and either falls off or remains withered upon the stalk; t juices which nourished it then go to the germ, to assist in its grow and enable it to become a perfect fruit.

Another use of the corolla seems to be, to furnish a resting-pla for insects in search of honey.

The corolla is supposed by Darwin to answer the same purpo to the stamen and pistils, as the lungs in the animal system ea petal being furnished with an artery which conveys the vegetab blood to its extremities, exposing it to the light and air under delicate moist membrane; this vegetable blood, according to h theory, is then collected and returned in correspondent veins, f

Papilionaceous-What corollas are anomalous?-Origin of the odour of flowers Odour affected by temperature-Odour affected by moisture-Odours sometimes di agreeable Dangerous if respired for a long time-Office of the corolla-Darwin theory with respect to the corolla.

the sustenance of the anthers and stigmas, and for the purpose of secreting honey.

Saint Pierre* thinks the corolla is intended to collect the rays of the sun, and to reflect them upon the stamens and pistils which are placed in the centre or focus.

After all our inquiries into the uses of the corolla, we are obliged to acknowledge that it appears less important, in the economy of vegetation, than many less showy organs. It seems chiefly designed to beautify and enliven creation by the variety and elegance of its forms, the brilliancy of its colouring, and the sweetness of its perfume. MMMM

Nectary.

In many flowers there is an organ called the nectary, which secretes a peculiar fluid, the honey of the plant; this fluid constitutes the principal food of bees and various other species of insects.

Linnæus considered the nectary as a separate organ from the corolla; and every part of the flower which was neither stamen,

pistil, calyx, nor corolla, he called a nectary; but he undoubtedly applied the term too extensively and vaguely. The nectary is not to be confined to any particular part of the flower. Sometimes it is a mere cavity, as in the lily. The crown imperial, Fig. 79, exhibits in the claw of each of its petals a nectary of this kind; each one being filled with a sweet liquid, the secretion of the flower. If these drops are removed, others immediately take their place. The six nectariferous glands at the base of the corolla are represented in the figure; the petals are supposed to be cut in order to show the base of the flower.

In the Ranunculus, (Butter-cup,) the nectary is a production of the corolla in the form of a scale; in the violet, a process of the same, in the form of a horn or spur. In the Columbine, (Aquilegia,) the nectary is a separate organ from the petals, in the form of a horn. In the monk's-hood, one of the petals being concave, conceals the nectaries; they are therefore said to be hooded.

In monopetalous corollas, the tube is supposed to answer the purpose of a nectary in secreting honey. In the honeysuckle, we find at the bottom of the tube a nectariferous liquid; yet there is no appearance of any gland or organ, by which it could have been secreted, unless we suppose the tube to have performed this office.

With respect to the purpose for which honey is secreted by the nectary and other parts of the flower, there seems, among authors, to be a difference of opinion. Darwin supposes this to be the food with which the stamens and pistils are nourished, or the unripe seeds perfected. Smith asserts, that the only use of honey, with respect to the plant, is to tempt insects, which, in procuring it, scatter the dust of the anthers, and fertilize the flower, and even carry the pollen from the barren to the fertile blossoms; this is particularly the case

*This ingenious author remarks, that man seems the only animal sensible to the sweet impressions made by the colour and odour of plants upon the senses; but we think he has asserted too much. Do not the brute creation seem to enjoy, by the sense of smelling, the freshness of the verdant fields? But man is very apt to say, See all things for my use.'

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St. Pierre's theory-Nectary-Its use-Not always a separate organ-Nectary of the crown imperial-Different forms of nectaries-Opinions of different writers respecting their use.

in the fig-tree. Although in the case of plants whose stamens a pistils are on separate flowers, we see this advantage arising fro the fact of insects being attracted by the honey, yet the great number of plants do not need any assistance in conveying pollen the stigmas. Some imagine that honey contributes to the perfecti of the stamens: but plants that do not appear to secrete honey, ha perfect stamens. One thing, however, is certain with respect to th fluid, that without detriment to the plant, it yields to the industrio bee the material for the manufacture of honey, a luxury high valued from the most ancient times. Virgil knew that bees ma honey from the juices which they gathered from flowers; and indeed, on this subject, know but little more than he has beautiful expressed in his pastorals.

Although we are ever discovering something new and wonder in the economy of nature; and, in some cases, seem permitted search into the hidden mysteries of her great Author, yet in our searches we are continually made sensible of the limited nature our own faculties; and a still, small voice, seems to whisper to ma in the proudest triumphs of his reason, "Hitherto shalt thou go, b

no farther."

LECTURE XIII.

STAMENS AND PISTILS.

ALTHOUGH the calyx and the corolla may be wanting, the stame and pistils are indispensable to the perfection of the fruit. They a in most plants enclosed by the same envelope, or stand on the san receptacle; in the class Monœcia they are on different flowers whi spring from one common root; and in Diœcia, they are on differe flowers, springing from different roots. Yet, however distant t stamens and pistils may be, nature has provided ways by which t pollen from the staminate flowers may be conveyed to the pistilla and there assist in perfecting the seed. That you may the bett understand this curious process, and the organs by means of whi it is carried on, we will examine each one separately.

Stamens.

Stamens are thread-like parts which are exterior with respect the pistil, and interior to the corolla. They exhibit a variety of p sitions with respect to the pistil. These positions seldom vary the same family, and they have therefore been taken by the cel brated Jussieu as one of the fundamental distinctions in his classi cation, called the "Natural method." If the stamens are insert upon the pistil, as in umbelliferous plants, they are said to be epig nous (from epi, upon, and gynia, pistil;) if the stamens are insert under the germ, as in cruciform plants, they are said to be hypog nous (from hypo, under, and gynia, pistil;) when the stamens are serted upon the calyx, and thus stand around the germ, as in the saceous plants, they are said to be perigynous, (from peri, around, a gynia, pistil.)

When a corolla is monopetalous, the number of the stamens sually, either equal, double, or half that of the divisions of the coroll the stamens in such flowers never exceed twenty.

Reflections-Stamens and pistils necessary to the perfection of the fruit-Defi tons of the stamen-Positions with respect to the pistil-Divisions of monopetalo Corollas usually in proportion to the number of stamens.

In polypetalous corollas, the number of stamens is sometimes much greater. When they equal the divisions of the corolla, they usually alternate with these divisions. When the number of stamens is double the divisions of the corolla, half of the stamens are usually placed in the intervals of the divisions, and the remaining half before each lobe of the corolla, corresponding to the intervals in the divisions of the calyx. If any of the stamens are barren or without anthers, they will be found to be those which are placed before the lobes of the corolla.

In commencing the analysis of flowers according to the Linnæan system, you learned that the number of stamens, their position, relatire length, and connexion, taken either singly or in combination, afford certain and distinctive marks for purposes of classification. In the first place we find the stamens differing in number, in different plants; some plants have but one, some two, and so on till we come to ten; when they have more than ten, we find the number in the same plant varies, and therefore we cannot depend on this circumstance for further classification.

We then resort to position, and consider whether the stamens are inserted upon the calyx or the receptacle, thus furnishing an eleventh and a twelfth class.

Inequality in the length of stamens, when they are either four or six, furnishes us with a thirteenth and fourteenth class.

The connexion or union of stamens gives us the fifteenth class, where the filaments of the stamens are united in one set; the sixteenth class, where they are in two sets; the seventeenth, where the anthers of the stamens are united.

The three remaining classes of phenogamous plants are distinguished by the position of the stamens with respect to the pistils. In the eighteenth class the stamens stand on the pistil; in the nineteenth the stamens and pistils are on separate flowers on the same plant; in the twentieth they are on separate plants; and in the twenty-first they are invisible.

Parts of the Stamen. The Filament, is so called from filum, a thread. Filaments vary in their form; some are long and slender, as in the pink; others are short and thick, as in the tulip. They are usually smooth, but in the mullein they are bearded; in the spiderwort (Tradescantia) they are covered with down. In most cases a filament supports but one anther, but sometimes it is forked and bears two or more; in some instances, many filaments have but one anther. When the filaments are enclosed in the tube of the corolla they are said to be inserted, when they extend out of it, exserted. In some cases the filament is wanting, and the anther is sessile, or immediately attached to the coralla.

In double flowers, the stamens, which seem to be intimately connected with the parts of the corolla, are changed to petals. This is the effect of cultivation, which, by affording the stamens excess of nourishment, causes them to swell out, and thus assume the form of petals. In some double flowers almost every trace of the stamens disappears; in others, it is easy to perceive the metamorphosis which they have undergone, as they retain something of their original forms. In double flowers the anthers usually disappear, which shows that the filaments have absorbed all the nourishment. In

Situation of the stamens with respect to the divisions of the corolla-Stamens used for purposes of classification-Differ in number-In their position-Stamens differ in length-In connexion-In position with respect to the pistil-Parts of the stamensFilament-Stamens changed to petals.

double roses some stamens appear entirely changed, others ret ing something of their form, and others are still perfect. When the stamens disappear, no perfect fruit is produced. On accoun this degeneration of the stamens, cultivated flowers are not usu so good for botanical analysis as wild ones. The single flower hibits the number of parts which nature has given to it. The 1 in its native state has but five petals.

Anther, is a little knob or box usually situated on the summi the filament; it has cells or cavities which contain a powder ca the pollen; this is yellow, and very conspicuous in the lily: tulip. You have here the representation (Fig. 80) of a stamen v

a Fig. 80. d

B1

B2

its filament a, its anther b, and the charging pollen c. In many flowers filament is wanting; the anthers are t said to be sessile; that is, placed im diately upon the corolla, as at d, wh represents a flower cut open, show its stamens growing sessile in throat.

Fig. 81.

The figure at A, presents a magnif stamen,* with a lan olate anther, denti late at the sides, w G two hairy appendag filament short.

At B 1, is a mag fied stamen,† with filament bearded at t base; the anther is tv lobed, reniform. I shows the two cells

Heach lobe, which is horizontally.

At C, the three fi ments are distinct at the base, and connected at the upper part; a thers, adnate, linear, twisting.

At D, the anther is sagittate, the filament bent, and glandular the middle, (at a.)

At E, is a stamen of the Thyme, (family of the Labiatæ ;) t lobes of the anthers c, are divergent; a, is the filament, b, the co nective of the anthers.

At F, is a stamen of the Laurus; a, cordate, pedicelled glands; pubescent filament; c, anther opening by four valves, throwing o pollen.

At G, is a stamen of the genus Lavendula; the anthers are re form, cilicate, opening transversely, lobes confluent at the summ divergent at the base.

At H, a stamen of the genus Begonia; the filament is enlarged the summit; the two lobes of the anther a, a, adnate at the side parallel distant.

*Of the Cerinthe major, (family of the Boragineæ.)

† Of the Tradescantia virginica.

Of the Cucumber family.

§ Of the Linden family.

Anther-Explain Fig. 81.