been placed. We thus form natural families. If the whole vegetable kingdom could thus be distributed into natural tribes, we should need no artificial system. But after selecting a few families, which exhibit striking marks of resemblance, we find genera whose re. lation to other genera seems doubtful or obscure, and at length find a vast number of plants which seem to have few natural affinities with any other.

Among resemblances which gives rise to natural families, are, 1st, resemblance in seeds,

2d, in pericarps, or the envelopes of seeds,

3d, in stamens and pistils,

4th, in corollas and calyxes,

5th, in the modes of infloresence, or the manner in which the flowers grow together upon the stalks,

6th, in leaves,

7th, in roots and stems.

In order to form a correct idea of the natural methods of classification, it is necessary to observe many plants, and the most constant characters of their organs. To find the place of plants in the artificial classes and orders, it is only necessary to observe the distinctions of the stamens and pistils.

The physician is chiefly conversant with the natural characters of plants, especially with such as are connected by medicinal qualities; he considers one group as narcotics; another as tonics; another as stimulants, &c.

The natural method depends for its utility, much upon the artificial system, which enables the student to ascertain the name of a plant, and thus learn its place among the natural orders. For example; suppose that a person meets with the plant commonly called stramonium, and wishes to know its character; by the Linnean System, he soon learns its botanical name, Datura; and this genus he finds belongs to the natural order, Solaneæ, characterized by qualities of an active and deleterious nature, as the Tobacco, Foxglove, &c.

The experienced botanist is not always obliged to refer to the artificial system for the natural character of an unknown plant. Being familiar with the characteristics of the different families, he can often determine at once by the habit or general appearance of the plant that it belongs to the lily tribe (Liliacea,) to the mallows tribe (Malvacea,) to the wild turnip tribe (Aroidea,) or to any other of the conspicuous and well-defined natural orders or families.

To Linnæus belongs the honour of having first suggested the arrangement of plants into natural orders.

He published in 1738 what he modestly termed "Fragments of a natural method," consisting of 58 orders, founded upon the resemblance of plants in their habits, general appearance, or medicinal qualities.

The most popular Natural method is that of Jussieu, a botanist of Paris, improved by De Candolle of Geneva.* The characters employed in this method, are,

1. The structure of the Seed, with respect to cotyledons. A plant * Professor Lindley of England, has recently published a work on the natural system, which is deservedly popular.

Resemblances which give rise to them-Physicians interested in the natural method -Connexion between the natural and artificial methods-Experienced botanists know plants by their habits-Natural method of Linnæus-Method of JussieuWhat are the characters employed in Jussieu's method?-How is the structure of the seed considered?

having no cotyledon is called, A-cotyledonous, with one, Mono-cotyledonous, and with two, Di-cotyledonous.

2. Insertion of the Stamens. The stamens are above the germ, under the germ; or around the germ; in the 1st case, they are Epi-gynous, 2d, Hypo-gynous, 3d, Peri-gynous.

3. Absence and presence of the Corolla. A-petalous, corolla wanting, Mono-petalous, corolla of one piece, Poly-petalous, many petals.

4. Union, or separation of Stamens and Pistils. Mono-clinious, stamens and pistils on the same corollas, Di-clinous, stamens and pistils on different corollas.

5. Union or separation of anthers. Anthers distinct, or anthers combined.

These classes were at first formed of 100 orders; under the present modifications of Jussieu's method they have been multiplied, by establishing new orders from genera which seemed not to belong to any of the former established orders.

The acotyledons include the cryptogamous plants of Linnæus. They are also called cellulares, from their being formed of cellular tissue without a vascular system. These are by some botanists called flowerless plants* their leaves are destitute of veins. They have no seeds with cotyledons, but are reproduced from a powderlike substance, exhibiting nothing of the parts which constitute the seeds in the other divisions of the vegetable kingdom.

The monocotyledons, which consist principally of grasses, palms, and liliaceous plants, are endogenous as regards the structure of their stems and branches;-the veins in their leaves, instead of being reticulate, or spreading out in various directions like a net, are straight and parallel. This division consists of two large groups;-1st, plants whose flowers have petals, called Petalloidæ, as the iris and lily; the calyx and corolla being in three or six divisions;-2d, where, instead of a proper calyx and corolla, the stamens and pistils are surrounded with glume-like bracts; these are called Glumaceæ ; as in the grasses.

The dicotyledons include all the phenogamous plants, except those which belong to the monocotyledonous division. These are vascular

It was long asserted by botanists, that every plant had a flower, although it might be invisible; but the term flowerless is now adopted by many for the cryptogamous family.

How the insertion of the stamens?-How is the corolla considered?-How the anther?-Repeat the synopsis of Jussieu's method--What are the general characteris tics of acotyledons ?-Of monocotyledons ?-Of dicotyledons?

in their structure, exogenous in their mode of growth, and their leaves are distinguished by branching, reticulate veins.

Comparison of the Methods of Tournefort, Linnæus, and Jussieu.

We have now presented the pupil with the outlines of three modes of classification, exhibiting the plant under a variety of aspects, calculated to give general and extended views of the subject, and at the same time impress the mind with a few important distinctions.

Tournefort dwells chiefly on different aspects and circumstances of the corolla ;-Linnæus, of the stamens and pistils ;—Jussieu, of the cotyledons and insertion of the stamens.

Of the comparative merits of these methods, we would observe, that Tournefort's cannot be relied on, because the forms of corollas are often indefinite, and vary into each other; that of Jussieu appears too abstract to be used independently of the aid of some more simple method:-the number of cotyledons, though a definite and important character, cannot, in many cases, be determined without the slow process of waiting for the seeds to germinate ;-the insertion of stamens and of the corolla often appears doubtful, even to the experienced botanist. Much as this method has been admired, it is but little used; while, on the contrary, that of Linnæus has, for more than half a century, been regarded as the key to botanical knowledge.

The characters used in his system are very apparent; and as it refers to the number of parts, rather than to their forms or insertion, it offers to the mind something positive, which is not found either in the method of Tournefort, or that of Jussieu. Between a corolla bellform, or funnel-form, there are many intermediate forms, which may be as much like one as the other. The insertion over the germ, or under the germ, are distinct, but the insertion around the germ sometimes blends with one, sometimes with the other mode. But between one or two stamens, or one or two pistils, there is no intermediate step, or gradual blending of distinctions, which leaves the student in doubt whether the case before him belongs to the one, or the other.

LECTURE XXII.

CHARACTERS USED IN CLASSIFICATION.

LINNEUS, in his "Philosophy of Botany," established three kinds of characters to be used in the description of plants.

1st. Factitious (or made.) That which is, by agreement, taken as a mark of distinction; thus, certain circumstances with respect to stamens and pistils are fixed upon for distinguishing classes and orders. Although nature has formed these organs, the arrangement of plants by their means is an invention of man, or artificial.

2d. Essential Character. That which forms á peculiar character of one genus, and distinguishes it from all other genera.

3d. Natural Character. This is difficult to define, though it is that which is understood by all; it is the general aspect and appearance of the plant, which enables all persons to make a kind of arrangement of plants in their own minds, although they would find it

What is the use of considering different modes of classification ?-What is said of the comparative merits of the three methods which are mentioned ?-System of Linnæus offers something positive-Three kinds of characters to be used in descriptions of plants-Factitious character-Essential character-Natural.

very difficult to explain their reasons for this classification to others. It will appear, from this definition of natural characters, that in some respects, the method of Jussieu is no less artificial than that of Linnæus, since it depends upon particulars which can only be learned and understood by the aid of science; and we must admit that the genera which its orders exhibit, are often as unlike, in habit and properties, as are those which compose the classes of Linnæus. It is by their natural characters, that persons who have never, perhaps, heard of such a science as zoology or the classification of animals, are enabled to distinguish ferocious beasts from domestic and gentle animals; they see a sheep or cow without any terror, although that individual one they may never have seen before; for nature teaches them to consider that as resembling other sheep and cows, which they know to be inoffensive. This natural character teaches savages to distinguish among the many plants of the forest, those which may administer to their wants, and those which would be injurious.

Even the lower grades of animals have this faculty of selecting by natural characters, nutritious substances, and avoiding noxious ones; thus we see the apparently unconscious brutes luxuriating in the rich pastures prepared for them by a benevolent Creator, and cautiously passing by the poisonous weed, directed by an instinct given them by this same Almighty Benefactor.

A natural family is composed of several genera of plants which have some common marks of resemblance, and its name is usually founded upon this general character; as Labiate and Cruciform, which are derived from the form of the corollas; Umbellate and Corymbiferous, from the infloresence; Leguminous, from the nature of the fruit. In many cases the family takes its name from a conspicuous genus belonging to it; as the Rosacea, or rose-like plants; Papaveracea, or poppy tribe, from Papaver, the poppy.

Natural families or orders resemble artificial orders in being composed of genera, but the principles on which these are brought together differ widely in the two cases.

In the truly natural families, the classification is such as persons who have never studied botany, might make; thus, dill, fennel, caraway, &c., belong to the Umbellate family, on account of the form in which the little stalks, bearing the flower, and afterward the seed, branch out from one common centre, like the sticks of an umbrella; this general resemblance being observable by all, it seems very natural to class such plants together.

But in the artificial orders, genera which may be very unlike in other respects, are brought together, from the single circumstance of plants having the same number of stamens and pistils. Thus, in the first order of the eighth class, we have the tulip and the bulrush, the lily of the valley and the sweet flag. In the second order of the fifth class, we have the beet and the elm. You will at once perceive the striking disparity between these plants, and that an arrangement, which thus brings them together, is properly called an artificial method.

Many families of plants possess a marked resemblance in form

Why is the method of Jussieu no less artificial than that of Linnæus ?-Animals distinguished by natural characters-Savages distinguish plants by these characters--Animals capable of discerning these natural characters-What gives name to a natural family of plants ?-In what respect do natural families resemble artificial orders?-How do they differ ?-Why may natural families be formed without a knowledge of botany?-Genera in the artificial orders brought together by having the same number of stamens and pistils.

and qualities, and appear evidently as distinct tribes. If the whole of the vegetable kingdom could thus be distributed into natural classes, the study of Botany would be much simplified; but it has already been remarked, that there are many plants which cannot be thus arranged, and no principle has yet been discovered for systematic arrangement which bears any comparison to the Artificial System. This system may be compared to a dictionary; though by its use we do not at first find the name for which we seek, and then learn its definition, as we do in dictionaries of terms; but we first learn some of the characters of a plant, and with these as our guide, we proceed to find the name. Having ascertained the botanical name, we can easily find to what natural family a plant belongs, and thus learn its habits, medicinal use, and other important particulars. The natural method may be considered as the grammar of botany; for between this, and the artificial system, the same relation exists, as between the grammar and dictionary of a language; it would be idle to attempt to decide on their comparative merits, since both are essential to science.

As the subject of classification is so important to a knowledge of botanical science, we will now consider the general principles on which it depends.

Rules.

1st. All botanical classification results from an examination and comparison of plants.

2d. Every organic distinction which establishes between individuals any resemblance, or any difference, is a character; that is, a sign by which they may be known and distinguished.

3d. The presence of an organ, its different modification and its ab sence, are so many characters.

4th. The presence of an organ furnishes positive characters, its absence negative characters.

Positive characters offering means of comparison, show the resemblances and differences which exist between individuals; those plants in which these characters present but slight differences should be collected in groups; those in which these characters differ more sensibly, should be separated; here we follow strictly the laws of the mind. But negative characters, as they allow no comparison, can only be employed to separate individuals, and never to bring them together.

When we say that plants have seeds with one or two cotyledons; that they have monopetalous or polypetalous flowers, and are provided with stamens and pistils, we point out particulars where visible and striking resemblances may be observed; these characters, then, are positive, since they are founded on something real.

When we say that some plants are destitute of cotyledon, corolla, stamens or pistils, we do not establish any real basis for the foundation of a comparison. If we wish to separate plants with monopetalous corollas, from such as have polypetalous corollas, this single character establishes, at once, the difference, which exists between the two groups, and the resemblance, which exists between individuals of each group. Thus positive characters possess a great advantage over negative ones; the latter should never be employed

Artificial system of arrangement compared to a dictionary-First learn the characters, then the name-The natural method considered as the grammar of botany— Mention the first four rules which are given for classification-Positive and negative characters-Give illustrations of these characters, with their uses-Advantage of positive characters over negative.