But this alternate movement of northern and southern declination has its limits; it stops at 23° 27' 30" on either side of the Equator; this, too, is the maximum of the distance which the imaginary axis of the photo-adumbrated sphere retires from the axis of terrestrial rotation; it is at the same time the value of the obliquity of the ecliptic, or of the inclined plane which the earth traverses in its annual movement of revolution.

Fig. 42 b, which represents the photo-adumbrated sphere at the summer solstice, will enable the reader to comprehend with the utmost facility the six months' day of the North Pole, coinciding with the six months' night of the South Pole; for the triangle N C D indicates the amount by which the illuminated moiety increases in the northern hemisphere between the spring equinox and the summer solstice, the amount being equal to that by which the adumbrated moiety overspreads in a contrary direction the South Pole in the southern hemisphere. The superfluous quantity of the photo-adumbrated sphere is nil at the apex of the two opposite triangles, or in the equinoctial region. And then, in effect, both day and night are always twelve hours long. Starting from the equinoctial line, we see how easy it is to calculate for each locality the variable dimensions of the arc which the sun, in its apparent course, traces above the horizon.

To see very distinctly the portion of the illuminated hemisphere, which, passing beyond the North Pole, forms a luminous course on the darkened moiety of our globe, I have but to place myself at midnight, on the 21st of June, in the prolongation of the terrestrial equator; in the same way, to see the corresponding portion of the darkened hemisphere, which advances beyond the South Pole to invade the illuminated, I have but to occupy at noon, on the 21st of June, a point of the same equatorial prolongation. Six months later, the same spectacle will be presented, inversely, on the 21st of December, in the southern hemisphere. See Fig. 43 a, where the pole N indicates the six months' day of the northern hemisphere (from the spring to the autumn equinox); while in Fig. 43 b, the pole S indicates the six months' night of the northern hemisphere (during the same period).

Now, no effort of the imagination is required to understand why the inhabitants of the northern hemisphere enjoy summer while those of the southern are enduring winter; why it is "blossoming spring" to the former when it is "purple autumn" to the latter, and vice versâ. Equally easy is it to comprehend why, after the equinox, day, or the duration of the sun above the horizon, gradually diminishes in one hemisphere and increases in the other; why, in summer, and in both hemispheres, the longest days alternate with the shortest nights, and in winter, the longest nights with the shortest days. It will not be more difficult to explain the cause of the prevailing cold in the polar zones, despite the prolonged sojourn of the sun above the horizon for a great part of the year. Observe how obliquely the solar rays are directed towards yonder shrouds of ice and snow: how can they warm them? They nearly all vanish into space. (See Fig. 42.)

Finally, there is not a phenomenon, even to that of dawn and twilight, which cannot, on these principles, be very fully and clearly explained. I have indicated, in a preceding paragraph, the rainbow-glories of colour noticeable on the line of demarcation between the illuminated and the darkened hemispheres. They are wanting where the rays of light strike vertically or nearly vertically. It is this circumstance which explains why, in the intertropical regions, the crepuscular phenomena are nearly null; why the sun, so to speak, sets and rises abruptly, like a taper which we extinguish or rekindle. These iris-gleams increase, on the other hand, in intensity, in proportion as we recede from tropical regions: the red touches the horizon, while the violet blends with the azure of the sky; between these two extremes, which are always very clearly marked, are arranged in less perceptible fashion, and in the order of refraction, the other colours of the rainbow.

What time and labour does it not require for the mind to disengage, to free itself from the fetters and incumbrances of sensorial appearances, the illusions of the senses, and to rise sufficiently high to seize at a glance all the dynamics of the world!

It is this faculty, however, which distinguishes the intellect from the imagination.

That he may abandon himself to the enjoyment of those pleasures which, like Dead Sea apples, crumble to ashes on his lips, the fool puts aside all mental toil, and disregards the shortness of his time,—ignores the brief period allowed for the development of the understanding. But, at least, let Imagination abstain from substituting its idle dreams for the assured results which can be only the reward of reason, conscientiousness, and labour! Unfortunately, here as elsewhere, it is vox clamantis, and we preach in the desert!

CHAPTER II.
WHAT MAY BE SEEN ON THE EARTH.

That the warning is true, all history attests. It is only, so to speak, from yesterday that the discovery of the sex of plants is to be dated; the tiny organs occupying the centre of the flower having always appeared so insignificant that they had passed, for some thousands of years, completely unnoticed. The eye of the spectator was caught by the calyx and the corolla; these envelopes, though of secondary importance so far as the reproduction of the vegetable is concerned, seemed to eyes dazzled by their glowing colours the true flower,—in fact, the entire flower. Science, which is the slow elaboration of thought matured by the study of objects of no human origin, has completely swept aside this premature judgment.

The Perianth.

We have already, and more than once, employed the word perianth[58] to designate the calyx or corolla, whether taken separately or together. In the former case, the perianth is simple; in the latter, it is double. A more appropriate word could not be made use of. It is derived from the Greek πεσὶ, around, and ἃνθος, flower; and literally signifies, "floral envelope." Simple or double, this envelope is the metamorphosis of several leaves, never of a solitary one, inserted upon planes so closely brought together that they seem confounded. Observe, in fact, how the leaves tend to efface their intervals on the blossom-bearing spray; they draw towards each other, they are apparently in eager haste to accomplish their destined transformation. What eloquence there is in this simple language of nature!

The Calyx.—The outermost whorl, or verticle, of the flower is called the calyx. And why? Out of a notion altogether incorrect. It is true that this foliaceous envelope may often assume the shape of a cup (in Latin, calix), and hence that the name has about it a semi-poetical air. But this only occurs when the calyx is composed of a single leaf, which has procured for it the special designations of monosepalous, gamopetalous, and monophyllous,—three different words expressing one and the same thing! The violet and the primrose are examples of a monophyllous, monosepalous, or gamopetalous calyx.

I see, dear reader, that you are puzzled by the word sepal. Certainly you would look for it in vain in any classical dictionary; it is neither Greek nor Latin. It was only invented, scarce a century ago, by a Swiss botanist, whose works have chiefly remained in manuscript,—by Necker, brother of the celebrated minister of Louis XVI., and uncle of the illustrious Madame de Staël. Let me explain the circumstance which determined, I suspect, the choice of this fanciful word,—a word belonging to no language but that of modern botanists.

The botanists of antiquity called the coloured leaflets of the corolla, petals. In this they were doubly right; for, first, they are, in reality, nothing but metamorphosed leaves; second, the word petal (in Greek, πέταλον) signified "a leaf" as early as the days of Homer, who, when speaking of the nightingale, says, like a keen observer of nature, that this bird, on the return of spring, sings—

The word petal was preserved by Tournefort, handed down by Linnæus and the two De Jussieus, and afterwards adopted by all botanists with the signification given to it by the ancients. Now, as the calyx may also consist of leaflets, which are generally green, Necker conceived the idea of applying to them the same term, after substituting an s for the initial letter p. Thus was created the word sepal. The innovation, I must point out, was not unanimously adopted. Many botanists continued to use the words "calicinal leaflets," introduced by Linnæus; others, though they adopted the innovation, protested against it.

But leaving the word, let us return to the thing.

The calyx consists originally of several leaflets. Is the monophyllous or monosepalous calyx a transformation due to the junction of the primitive leaflets? Observation replies in the affirmative.

In the formation of junctures or adhesions nature proceeds from beneath to above. Our language proceeds inversely to nature: we speak of a lobed, dentated, or partite calyx, as if it were primarily monophyllous, and its more or less profound divisions (indicated by the words "lobed," "dentated," "partite") were but consecutive results, produced from above to below.

The truth is, that the calicinal divisions, which we call lobes, lacinias, and the like, are but the tops of leaflets united at their base. The monophyllous calyx (formed of one piece) is, therefore, simply the result of a more or less complete union of the leaflets composing, properly speaking, the calicinal whorl. This whorl is originally polyphyllous; that is to say, formed of several distinct parts. If it were, in the first place, monophyllous, it would be impossible to understand how its divisions are made from top to bottom, since nature, in its developments, proceeds from bottom to top. In the final analysis, then, it is an error to consider the calyx as a cup, primarily formed of a single piece.

Grew, an English botanist of the eighteenth century, seems to have been the first who made use of the word calyx. "I call a calyx," he says,[60] "the external portion of the flower, which enfolds the others, whether it be all in one piece, as in the violets, or divided, as in the roses."

If we wish to conform to the truth, as brought before us by nature, we must revolutionize our terminology. Instead of speaking of bipartite, tripartite, quadripartite, or of bilobed and trilobed calices,—terms all signifying that the monophyllous calyx is cloven more or less deeply from top to bottom, we must say that the calyx in such and such a species has its leaflets united at the base, or one third, fourth, or half of its height; the polyphyllous or polysepalous calyx will be that whose leaflets remain detached, as was the case in the monophyllous or monosepalous calyx. This language, recommended by the authority of Auguste Saint-Hilaire, would be more precise and exact: therefore, it will not be very quickly adopted. One would say that the human mind condemns itself to pass through the purgatory of what is false and complex, before resolving to adopt the simple and the true.

If we admit the theory according to which all the organs of the vegetable are the result of a metamorphosis of the leaf, we shall ask what place is to be given to the calyx in the series of these transformations?—Answer: The calyx is a foliaceous transformation, intermediary between the bracts and the corolla.

It is particularly in the study of the calyx that the attentive eye is struck by those proteiform movements in which nature makes sport of our absolute rules.

For example: in the Berberis vulgaris, the young calicinal leaflets have less resemblance to the bracts than to the petals of the corolla, and hence they have received the name of petaloid sepals. In other flowers this morphogenic wavering inclines towards the bracts rather than towards the corolla. We hesitate, therefore, whether we must give the name of calyx or bracts to the three under leaflets which are visible beneath the petaloid envelope of the Anemone nemorosa, or wood anemone. The calyx of the Celandine (Ranunculus ficaria), which also flowers in spring, is exactly like a whorl or involucre formed by the union of the bracts.

A similar embarrassment takes place when the calyx, in its metamorphosis, inclines too visibly in the direction of the corolla. Thus, in the Polygala vulgaris,—a little, vivacious, and very abundant plant,—the two inner leaflets of the calyx are not only larger than the three other outer leaves, but they are coloured like the petals, and become, towards the close of their flowering time, membranous, herbaceous, and marked with three strong veins: they resemble the wings of a butterfly, and have been called wings.

These peculiarities are useful in the distinction of certain species, which, at bottom, are simply varieties. Thus, in the Polygala Austriaca (Polygala amara of Keoch, Polygala uliginosa of Reichenbach),—a plant with small white or bluish leaves, which is sometimes met with on the borders of peaty swamps,—the central vein or ridge of the wings is simple, and never anastomoses with the lateral veins; while, in the Polygala vulgaris, as well as in the Polygala depressa and Polygala amarella, the vein is ramified, and anastomoses more or less widely with the laterals.

But since we are upon this subject, why should we not seize the opportunity of familiarising ourselves, under the form of a digression, with the little family of the Polygalaceæ? But no; we will adjourn the episode, since it would cut the thread of our discourse upon the calyx, our calicology.

Some calices there are, which, by their colouring, approximate so closely to the second floral envelope, that one is always tempted to call them corollas.

Such are:—The red calyx of the fuchsia;

The yellow calyx of the furze (Ulex Europæus), and of a kind of hellebore (Helleborus hyemalis);

The rosy calyx of the Christmas rose (Helleborus niger);

The blue calyx of the larkspur (Delphinium Ajacis); and the Napel aconite (Aconitum Napellus).

In the Aquilegia vulgaris, and in the Trollius Europæus, the calyx, by the form and colouring of its leaflets, is confounded with the second whorl so completely, that Linnæus gave it the name of corolla.

Nevertheless, in the midst of these waverings, which lead us to mistake the calicinal leaflets sometimes for bracts, sometimes for petals, we recognise perfectly the foliaceous type. Independently of its colour, which is generally green, the calyx has the same organisation as the leaf; we find in it the same tracheæ and the same stomata, the same glands and the same hairs; the veins and ramifications are also the same; and, in more than one instance, the calicinal leaflet resumes the character of a veritable leaf. Look, for example, at the five leaflets, united so strongly at the base but so free at the top, arranged in the form of a quincunx, of the hundred-leaved rose. The two external, enlarged, and lanceolate pieces are garnished on the right and left, and often at the point, with tiny foliaceous appendages, which, in every respect, imitate the composite leaf that carries the slender stem. And if we move aside the external or bearded parts of the calyx, we see that the internal bear less and less resemblance to a leaf. Thus, the part which comes next is semi-bearded; that is to say, it is furnished with foliaceous appendages only on one side; and the two upper pieces are beardless, that is, reduced to the dilated central vein.

It was these metamorphic forms of the free portion of the calicinal foliola (united below) of the rose, which originated a well-known enigma, conveyed in the following Latin distich:—

("We are brothers, both bearded, two beardless; I am two half-bearded, and I myself am half-bearded.")

They are specially noticeable in a variety of the Rose of Bengal, in which all the petals seem to be transformed into calicinal leaves. (Fig. 44.)

The part of the calyx formed by the union of the sepals is called the tube: it is invariably the lower part. The upper portion, where the sepals are free, is the limb.

Throughout the vegetable kingdom you will not find a calyx in which the union of the sepals takes place at the top.

This time, at all events, we have found—what is exclusively rare in nature—a rule without an exception.

Generally, it is almost impossible to disunite, without rending, the foliola composing the tube of the calyx, their union is so complete. This circumstance prevented the first observers from accurately apprehending the composition and true development of the calyx. There are cases, nevertheless, in which Nature—the coquette!—suffers herself to be surprised, if her lover have patience. As an example we shall cite the monophyllous calyx of the Œnotheræ.

Let us take the species known as Œnothera biennis. It belongs, with the fuchsia, circæa, trapa, and others, to the Evening Primrose family, or Onograceæ.

Its pale yellow blossoms are unfolded during the hush of evening-time in almost every garden, shedding abroad on the breeze its delicate but delicious odour. Its petals open in a remarkable manner. The calyx, as we shall see, has small hooks attached to its upper extremity, by which it holds the flower together before expansion. The calicinal divisions gradually unfold at the lower part, and reveal the yellow flower, which remains awhile closed at the upper parts of the hooks. The flower then suddenly opens half-way, when it stops; afterwards completing its expansion gradually, and finally opening with a loud noise.

This curious plant is of American origin, and was unknown in our country until 1674, when it was introduced by some French floriculturists.

It opens generally at about six or seven o'clock in the evening.

And this statement induces me to digress. Where can I better introduce to the reader's notice a Floral Dial? It is not so complete as it might be made if I had space to enlarge upon the subject. My object, however, is simply to suggest; and this brief allusion to the hours at which flowers fold and unfold may induce the reader to study in more detail a very pleasant branch of botanical science. He will find full particulars in Mr Loudon's excellent "Encyclopædia of Gardening."

It is generally stated that the first Floral Dial, or clock, which showed the time by the opening or shutting up of blossoms throughout the day, was a fancy or invention of the great Swedish naturalist, Linnæus. But there is a distinct allusion to this poetical measurement of the "fleeting hours" in Marvell's poem on "The Garden:"—

Whether the idea first occurred to Englishman or Swede, poet or botanist, matters but little; it is a graceful, a suggestive, a beautiful idea, and might well be reproduced in some of our large public gardens.

FLORAL DIAL.

TIME AT WHICH THE FOLLOWING FLOWERS FOLD AND UNFOLD.

After this long digression, we return to our Evening Primrose.

Its large yellow flowers are disposed in clusters at the top of a stem often twenty inches long. The Pythagorean tetrad (i.e., the number 4 and its double) predominates in all its organs: 4 stigmata crowning a filiform stylus; quadrangular capsule with 4 polyspermous lobes; opening at top by the separation of 4 valves; twice 4 stamens; 4 petals on a large, emarginated limb; 4 sepals. These are united at the base, but not so as to prevent the observer from distinguishing their number.

The general terms "regular" and "irregular," applied to the calyx, as to every other organ, require to be employed with considerable reserve. The delicate shades, which ought to separate regularity from irregularity, are often so inappreciable that it is almost impossible to say where one begins and the other ends. See, for example, the Labiatæ. In most genera and species of this family, the two lips, one of which consists of two and the other of three foliola, bring out very completely the inequality of the calyx. But there are also Labiatæ, the inequality of whose sepals completely effaces the character of the irregular bilabiated calyx.

In certain inflorescences, where the flowers comprising them are very close together, as, for example, in the capitules of the Synantheraceæ, the free upper portions of the calyx may take the most irregular forms; as, sometimes, a tuft, simple or feathery; sometimes, membranous or scarious spangles; and, sometimes, bristles of greater or less stiffness. What elements of the calyx do these transformations represent? The veins, and notably the midrib of the limb of the sepals, united underneath.

The free foliola of the polyphyllous calyx may vary in form, like the caulinary leaves whence they issue by way of metamorphosis; they may be oval, elliptical, linear, &c. Yet none have ever been observed of a heart-shape (cordiform).

Certain foliola of the polyphyllous calyx affect fantastic outlines. In the Delphinium, the upper sepal is prolonged into a spur. In the aconites it is hollow like a helmet. The spur of the calyx of the monk's-hood (Capucine) is the result of the united prolongation of these foliola. The buckler (Scutellum), from which is named the Scutellaria, a genus of Labiatæ, is a demi-orbicular boss formed below the inferior lip of the calyx.

The union of the calicinal foliola sometimes forms a conical calyx, as in the Silena conica, and sometimes a cup-shaped calyx, as in the orange; sometimes, moreover, an urceolate calyx, as in the henbane (Hyosciamus niger). These forms may vary singularly. The calyx of the black alder (Rhamnus frangula) is shaped like a top; that of the haricot (Phaseolus vulgaris), like a bell; that of the tobacco-plant, or the Mollucella spinosa, is infundibuliform (or funnel-shaped).

The observer is sometimes embarrassed in deciding to which whorl he should refer the foliola he is examining. Thus, the tiny foliola which, in the strawberry and the potentilla, alternate with others and larger ones, are stipules rather than sepals. Ought the sepals of the calyx in the Malvaceæ to be assimilated in like manner to the stipules? It is difficult to reply to this question satisfactorily. Take, for example, the Hibiscus Syriacus, an ornamental shrub, better known by the name of the garden-hemp. The inner calyx, or calyx properly so called, of this Malvacea has five sepals, while the outer calyx, or calicule, has twelve. Now, a leaf cannot have more than two stipules, one on each side. For an outer calyx, then, the proper number of foliola is ten, not twelve. To look upon the second calyx as a "supernumerary development," would be to hazard a supposition contrary to the unity of plan of the floral organs.

The calyx, like the corolla, is not an absolutely indispensable organ. Sometimes, therefore, it is caducous—that is, falls off before the flower expands,—as in poppies; sometimes, persistent, or remains after flowering,—as in roses and the majority of plants. In some cases it is persistent only until after the act of fecundation, but this act accomplished, it falls with the corolla in most of the Cruciferæ and Ranunculaceæ. This is a deciduous calyx.

The "caducity" and "persistency" of floral envelopes furnish some valuable characteristics for the distinction of species. Thus, two closely-allied Cruciferæ, the Alyssum calicinum, so common in spring upon stony soils, and the Alyssum montanum, can only be distinguished from one another by the fact that the calyx of the former is persistent, of the latter caducous. It is true that the flowers of the Alyssum calicinum are of a yellow which easily passes into white, while those of the Alyssum montanum are of a beautiful permanent yellow. But this latter distinction is not so good as the former.

The persistent calyx sometimes assumes a considerable increase of very common appearance. For example, take the Physalis alkekengi, a member of the Nightshade family or Solanaceæ. The red bladder-like accrescence surrounding the scarlet fruit is the calyx, which, after flowering, has grown much larger than it was before. And these bright flowers which resemble large strawberries, and abound on the borders of meadow-paths, if you look at them closely, you find to be the accrescent calices of the Trifolium fragiferum. The very word fragiferum reminds us of the strawberry.

The calyx may change in consistency and texture in proportion as the ovary, to which it adheres, changes into fruit. The fleshy pulpy substance of the apple, and, in general, of the fruits of the Pomaceæ, is simply an excessive development of the calicinal tube united all around the ovary, and recognisable in the pips, imprisoned, towards the centre, in horny lobes. In other plants, as the flower develops into fruit, the calyx becomes woody: such is the case with the Water Chestnut (Trappa natans).

Finally, the calyx may even contribute to the dissemination of the seed. We may cite, as an example, a Brazilian species of Urticaceæ, which Saint-Hilaire named the Elasticaria. The fleshy and cylindrical parts of the calyx are curved inwards, and thus defend, as one might do with one's bended fingers, the young fruit until it is completely developed; as soon as the fruit is ripe, they spring up erect, and launch it to a distance.

The Corolla.—If from the circumference we proceed to the centre of the flower, the calyx being the first, the corolla will be its second envelope.

If, on the contrary, we proceed from the centre to the circumference, the corolla will form the fourth whorl; the pistil (consisting of stigmata, stylus, and ovary) being the first; the nectariferous disc (often wanting) the second; and the stamens the third whorl. Remarkable for its varied tints, the corolla, to indifferent or ignorant eyes, seems the entire flower.

A black or blackish colour is exceedingly rare. Out of 300 vegetable species which compose the flora of Central Europe, there are not six with blackish or even grayish flowers. No hypothesis has yet been put forward to explain this mark-worthy rarity.

Species with a yellow corolla are the most numerous, forming more than a sixth of the European flora: then come, in their order of frequency, species with green, white, red, and blue flowers; the white increasing in number as we approach the Pole.

Dividing the flora into twenty parts, we may ascribe to each colour, and its various tints, the following proportion:—

The analogy between the parts or petals of the corolla and the leaf, is perhaps not quite so striking as between the leaf and the sepals of the calyx. The phrase "rose-leaves" is an expression consecrated by immemorial usage. Why not prefer the term "corollary leaves or leaflets (foliola)" to that of petals?

The corollary leaves, or petals, are organised like true leaves. They have the same system of venation; their lamina correspond to the "limb," or "blade;" and their unguis, or "claw," to the "petiole," or stalk. (See Fig. 46, a.) The upper margin of petals is frequently more obtuse than the overspreading margin of the blade of a leaf, which, in most cases, is pointed. Non-unguiculate petals represent the sessile leaves. (Fig. 46, b.) Their form is much more varied than that of the calicinal foliola, which are never unguiculate or petiolated.

The petal is defined as regular when its two halves, folded one upon another at the midrib, exactly cover each other; in the opposite case it is called irregular. In certain species, the petals are furnished with characteristic appendages. But observe, these appendages, which generally affect the form of a spur, have no character of generality. Thus, for example, in the violet, a single petal is prolonged into a spur below its point of attachment; in larkspur, and the other Delphiniums, there are two which terminate in the same manner; in the Aquilegia vulgaris, all the petals are calcarate (calcar, a spur).

According as the veins of the petal proceed in a straight or curved direction, its limb may be flat, or concave, or hollowed like a boat—i.e., cymbiform (cymba, a boat), or naviculate (navis, a ship), or like a spoon, cochleariform (cochleare, a spoon). When the spur is very short, as in Antirrhinum and Valerian, the corolla or petal is termed gibbous (gibbus, a swelling), or saccate at the base.

If a petal continue narrow, so as to seem formed by the prolongation of the claw, it is called linear; if the limb be prolonged below, so as to form two lobes, it is cordate, as in Genista caudicans; or if the lobes be acute, it may be sagittate or hastate.

The number of petals varies from two to twelve, and more. A corolla with a single petal, unipetalous, which we must not confound with the monopetalous corolla, is a monstrosity, created by defective development; the other petals or foliola are abortive. A corolla with two petals, or dipetalous, as in Circæa Lutetiana, is rare. A tripetalous corolla occurs only when the calyx has likewise three foliola. But in this instance opinions are divided: the majority will not admit more than a single floral envelope,—a perianth of six foliola, of which three, herbaceous and internal, alternate with three petaloid and external.

Many of our aquatic plants may be quoted as examples: such as the Butomus umbellatus, or flowering rush; the little frog-bit, or Hydrocharis morsus ranæ; and the water plantain, Alisma plantago.

The tetrapetalous (or four-petalled) corolla is usually arranged like a cross, and is much more frequent than the dipetalous or tripetalous; for examples, we need only refer to the large and important family of the Cruciferæ.

The number five (pentapetalous) is still more common; but we meet with it in other organs besides petals, and it seems particularly characteristic of the vegetable kingdom.

Thus, all the Umbelliferæ have five sepals, five petals, and five stamens; in all the Crassulaceæ, the number five applies, not only to the sepals and the petals, as well as to the stamens, but also to the carpels which compose the ovary.

Corollas with six, eight, nine, ten, or twelve petals are relatively rarer; and when the petals become so numerous that we cannot count them, we have to deal with transformations of stamens into petals, with those monstrosities of cultivation which we call double flowers, flores pleni, where all the male organs have disappeared,—flowers wholly unfit for fructification.

The petals of the corolla are not always free. Like those of the calyx, they may be attached to one another by their edges, but this union invariably takes place, as in the former, from bottom to top. Therefore, we never see any petals united at the top, and disengaged at the bottom (see Fig. 47, a.) But the reader must take careful note that this invariable characteristic is not peculiar only to the floral envelopes; it is not met with in the stamens, for these may be united, either by their anthers, as in the whole family of the Synantheræ, or by their filaments, as in the Leguminosæ. And what we have said of the stamens applies also to the parts constituting the pistil. This radical difference between the perianth and the true reproductive organs ought, from the beginning, to have fixed the attention of botanists on the centripetal and centrifugal metamorphosis of the leaf, which we have spoken of in "The Circle of the Year."

In many plants we are permitted to follow step by step, as it were, the union of the petals, and their definitive transformation into what is called the monopetalous corolla. The term monopetaloid ought then to be rejected, if we are to believe that the monopetalous corolla is the result of the metamorphosis of a single leaf. The word gamopetalous, or, rather, gamophyllous, is preferable. As we have remarked in reference to the calyx, we shall here repeat that the expressions bilobed, trilobed, quadrilobed, or bipartite, tripartite, quadripartite corollas, are radically vicious, because they are the consequence of a false point of view, according to which the monopetalous corolla will be simply a single metamorphosed leaf, susceptible of being more or less deeply divided from top to bottom.

The polypetalous corolla, as well as the gamophyllous corolla, may be regular or irregular, according as the foliola are equally or unequally united. But here again we must be careful not to lay down too absolute rules. Examine, for instance, the gamophyllous corolla of the gentians; their two lobes are very unequal, and yet the corolla is regular: five very large lobes alternate with five very small, in such wise that each of the latter is situated between two larger lobes. Each division of the corolla of the periwinkle is irregular, and yet the aggregate of their divisions is regular: these are all of the same form and the same size.

In the gamophyllous corolla we are able to discern, through the different forms it assumes, the form of the parts which compose the union. Thus, for example, the tubulate corolla supposes the pre-existence of unguiculate petals.

Inequality of union produces the bilabiate corolla, which is invariably tubular. This is the case in the natural family of the Labiatæ. The upper lip is composed of two petals, and the lower of three. The parts of the upper are sometimes so closely joined that they appear to be but one, as in the Lamium; and the lower often becomes quadrilobed by the division of the middle petal, as in the Stæcha.

In the labiated corolla, the mouth of the tube is open, while in the personate or masked (persona, a mask) it is closed by the pressure of the lower lip against the upper; as in Snapdragon and Frogsmouth, the projection of the lower lip being called the palate. By this feature the family of the Scrophulariaceæ is easily distinguished from that of the Labiatæ.

In some corollas, the two lips are hollowed out in a very singular fashion, as in the Calceolaria; assuming a "slipper-like appearance," similar to what takes place in the labellum of certain orchids,—to wit, the Cypripedium. These calceolate (calceolus, a slipper) corollas may be looked upon as consisting of two slipper-like lips.

The forms of the bilabiate, tubular, and ligulose florets, of the capitula of the Synantheræ, are likewise due to simple differences of union. The floscular capitulum comprises the tubular florets, and the semi-floscular capitulum, the ligulate florets; the radiate capitulum consists of florets ligulate or bilabiate at the circumference, and of tubular florets over the rest of the receptacle. By considering the capitula, as the vulgar do, to be flowers, Tournefort introduced considerable confusion into the nomenclature of the Synantheræ.

SUMMER FLOWERS.