An introduction to physiological and systematical botany/Chapter 23
CHAPTER XXIII.
EXPLANATION OF THE LINNÆAN ARTIFICIAL SYSTEM.
The Linnæan System is, as I have already observed, professedly artificial. Its sole aim is to help any one to learn the name and history of an unknown plant in the most easy and certain manner, by first determining its Class and Order in this system; after which its Genus is to be made out by comparing the parts of fructification with all the generic characters of that Order; and finally its Species, by examining all the specific definitions of the Genus. We thus ascertain the generic and specific name of our plant in Linnæus, and under those we find an enumeration, more or less ample, of its Synonyms, or the different appellations it has received from other writers, with a reference to figures in various books; and as Linnæus always cites Bauhin's Pinax, which is the common botanical catalogue, or index to all previous works, we thus gain a clue to every thing recorded concerning our plant. Of all this mass of information and entertainment we shall find nothing more concise, luminous, or engaging, either with respect to the distinctions, uses, or history of plants than what is diffused through the various publications of Linnæus himself; and the same may, with
at least equal truth, be said of those of his works which illustrate the Animal kingdom. His magic pen turns the wilds of Lapland into fairy land. He has all the animals of Sweden as much at his call, as our first parent while the terrestrial paradise was yet in primæval tranquillity. No writer whatever has rendered the natural productions of the happiest and most luxuriant climates of the globe half so interesting or instructive as Linnæus has made those of his own northern country.
The Classes of the Linnæan System are 24, and their distinctions are founded on the number, situation, or proportion of the Stamens. The Orders are founded either on the number of the Pistils, or on some circumstance equally easy, which we shall in due time explain.
The first eleven Classes are characterized solely by the number of the Stamens, and distinguished by names, of Greek derivation, expressive of these distinctions.
1. Monandria. Stamen 1. A small Class.
2. Diandria. Stamens 2.
3. Triandria ━━━━ 3.
4. Tetrandria ━━━━ 4.
5. Pentandria ━━━━ 5. A numerous Class.
6. Hexandria ━━━━ 6.
7. Heptandria ━━━━ 7. A very small Class.
8. Octandria ━━━━ 8.
9. Enneandria ━━━━ 9. A small Class.
10. Decandria ━━━━ 10.
11. Dodecandria ━━━━ 12 to 19.
12. Icosandria ━━━━ 20 or more Stamens, inserted into the Calyx. Here we first find the situation of the Stamens taken into consideration. They grow out of the sides of the Calyx, often from a sort of ring, as in the Strawberry. This is truly a natural Class, as are several of the following ones; so that in these instances the Linnæan method of arrangement performs more than it promises. The character of this Class is the more important, as such a mode of insertion indicates the pulpy fruits which accompany it to be infallibly wholesome, and this holds good, not only when the stamens are numerous, but in all other cases. Thus Ribes, the Currant and Gooseberry genus, whose 5 stamens grow out of the calyx, stands in the fifth class, a wholesome fruit, among many poisonous berries. No traveller in the most unknown wilderness need scruple to eat any fruit whose stamens are thus situated; while on the other hand he will do well to be cautious of feeding on any other parts of the plant.
13. Polyandria. Stamens numerous, commonly more so than in the last Class, and inserted into the Receptacle, or base of the flower, as in the Poppy, Anemone, &c. The plants of this fine and numerous Class are very distinct in nature, as well as character, from those of the Icosandria.
14. Didynamia. Stamens 2 long and 2 short. Here proportion comes to our assistance. This is a natural Class, and contains most of the labiate, ringent or personate flowers, as the Dead-nettle, Snap-dragon, Fox-glove, &c.
15. Tetradynamia. Stamens 4 long and 2 short. A very natural Class, comprehending all the Cruciform flowers, as the Wall-flower, Stock, Radish, Mustard, &c. Cleome only does not properly belong to the rest.
16. Monadelphia. Stamens united by their filaments, more or less extensively, into one tube, as the Mallow tribe, in which such union is very remarkable, and the Geranium family, in which it is less evident.
17. Diadelphia. Stamens united into 2 parcels, both sometimes cohering together at the base. This Class consists of Papilionaceous flowers, and is therefore natural, except that some such genera having distinct Stamens are excluded, and referred to the tenth Class, in consideration of their number solely; as some ringent flowers with only 2 Stamens are necessarily placed, not in the 14th Class, but the 2d.
18. Polyadelphia. Stamens united into more than 2 parcels, as in St. John's-wort. A small Class, in some points related to Icosandria.
19. Syngenesia. Stamens united by their Anthers into a tube, rarely by their Filaments also; and the flowers are Compound. A very natural and extremely numerous Class. Examples of it are the Dandelion, Daisy, Sunflower, &c.
20. Gynandria. Stamens united with, or growing out of the Pistil; either proceeding from the Germen, as in Aristolochia, Engl. Bot. t. 398, or from the Style, as in the Orchis family. The Passion-flower is wrongly put by Linnæus and others into this Class, as its stamens merely grow out of an elongated receptacle or column supporting the Germen.
21. Monoecia. Stamens and Pistils in separate flowers, but both growing on the same plant, or, as the name expresses, dwelling in one house, as the Oak, Hazle, and Fir.
22. Dioecia. Stamens and Pistils not only in separate flowers, but those flowers situated on two separate plants, as in the Willow, Hop, Yew, &c.
These two last Classes are natural when the barren flowers have, besides the difference in their essential organs, a different structure from the fertile ones in other respects; but not so when they have the same structure, because then both organs are liable to meet in the same flower. In some plants, as Rhodiola, Engl. Bot. t. 508, each flower has always the rudiments of the other organ, though generally inefficient.
23. Polygamia. Stamens and Pistils separate in some flowers, united in others, either on the same plant, or on two or three different ones.
This Class is natural only when the several flowers have a different structure, as those of Atriplex; but in this genus the Pistil of the united flower scarcely produces seed. If, with Linnaeus, we admit into Polygamia every plant on which some separated barren or fertile flowers may be found among the united ones, while all agree in general structure, the Class will be overwhelmed, especially with Indian trees. I have therefore proposed that regard should be had to their general structure, which removes all such inconvenience, and renders the Class much more natural.
24. Cryptogamia. Stamens and Pistils either not well ascertained, or not to be numbered with any certainty, insomuch that the plants cannot be referred to any of the foregoing classes. Of this Ferns, Lichens, Sea-weeds and Mushrooms are examples.
Appendix. PALMÆ, Palm-trees, a magnificent tribe of plants, chiefly tropical, whose flowers were too little known, when Linnæus wrote, to serve the purposes of classification; but they are daily clearing up, and the Palms are found generally to belong to the Classes Monoecia, Dioecia, or Hexandria.
The Orders of the Linnæan System are, in the first 13 Classes, founded on the number of the Styles, or on that of the Stigmas when the Styles are wanting, which occurs in Viburnum. Such Orders are accordingly named
Monogynia. Style, or sessile Stigma, 1.
Digynia. Styles, or sessile Stigmas, 2.
Trigynia ━━━━━━━━━━━━━━━━ 3.
Tetragynia ━━━━━━━━━━━━━━━ 4.
Pentagynia ━━━━━━━━━━━━━━━ 5.
Hexagynia ━━━━━━━━━━━━━━━ 6, of very rare occurrence.
Heptagynia ━━━━━━━━━━━━━━ 7, still more unusual.
Octagynia ━━━━━━━━━━━━━━━ 8, scarcely occurs at all.
Enneagynia. Styles, or sessile Stigmas, 9, of which there is hardly an instance.
Decagynia ━━━━━━━━━━━━━━━━━ 10.
Dodecagynia ━━━━━━━━━━━━ about 12.
Polygynia ━━━━━━━━━━━━━━━━ many.
The 2 Orders of the 14th Class, Didynamia, both natural, are characterized by the fruit, as follows;
1. Gymnospermia. Seeds naked, almost universally 4.
2. Angiospermia. Seeds in a capsule, numerous.
The 2 Orders of the 15th Class, Tetradynamia, both very natural, are distinguished by the form of the fruit, thus:
1. Siliculosa. Fruit a Silicula, Pouch, or roundish Pod.
2. Siliquosa. Fruit a Siliqua, or long Pod.
The Orders of the 16th, 17th and 18th Classes, Monadelphia, Diadelphia and Polyadelphia, are founded on the number of the Stamens, that is, on the characters of the first 13 Classes.
The Orders of the great natural 19th Class, Syngenesia, are marked by the united or separated, barren, fertile, or abortive, nature of the florets.
1. Polygamia æqualis. Florets all perfect or united, that is, each furnished with perfect Stamens, a Pistil, and one Seed.
2. Polygamia superflua. Florets of the disk with Stamens and Pistil; those of the radius with Pistil only, but each, of both kinds, forming perfect Seed.
3. Polygamia frustranea. Florets of the disk as in the last; those of the radius with merely an abortive Pistil, or with not even the rudiments of any. This is a bad Order, for reasons hereafter to be explained.
4. Polygamia necessaria. Florets of the disk with Stamens only, those of the radius with Pistils only.
5. Polygamia segregata. Several flowers, either simple or compound, but with united anthers, and with a proper calyx, included in one common calyx. Linnaeus has a 6th Order in this Class, named Monogamia, consisting of simple flowers with united anthers; but this I have presumed to disuse, because the union of the anthers is not constant throughout the species of each genus referred to it, witness Lobelia and Viola, while on the contrary several detached species in other Classes have united anthers, as in Gentiana, Engl. Bot. t. 20. These reasons, which show the connection of the anthers of a simple flower to be neither important in nature, nor constant as an artificial character, are confirmed by the plants of this whole Linnæan Order being natural allies of others in the 5th Class, and totally discordant, in every point, from the compound syngenesious flowers.
The Orders of the 20th, 21st and 22d Classes are distinguished by the characters of some of the Classes themselves which precede them, that is, almost entirely by the number of their Stamens; for the union of the anthers in some of them is, for the reasons just given, of no moment.
The Orders of the 23d Class, Polygamia, are, according to the beautiful uniformity of plan which runs through this ingenious system, distinguished upon the principles of the Classes immediately preceding.
1. Monoecia has flowers with Stamens and Pistils on the same plant with others that have only Pistils, or only Stamens; or perhaps all these three kinds of blossoms occur; but whatever the different kinds may be, they are confined to one plant.
2. Dioecia has the two or three kinds of flowers on two separate plants.
3. Trioecia has them on three separate plants, of which the Fig is the only real example, and in that the structure of the flowers is alike in all.
The Orders of the 24th Class, Cryptogamia, are professedly natural. They are 4 in Linnæus, but we now reckon 5.
1. Filices. Ferns, whose fructification is obscure, and grows either on the back, summit, or near the base of the leaf, thence denominated a frond. See p. 133.
2. Musci. Mosses, which have real separate leaves, and often a stem; a hood-like corolla, or calyptra, bearing the style, and concealing the capsule, which at length rises on a stalk with the calyptra, and opens by a lid.
3. Hepaticæ. Liverworts, whose herb is a frond, being leaf and stem united, and whose capsules do not open with a lid. Linnæus comprehends this Order under the following.
4. Algæ. Flags, whose herb is likewise a frond, and whose seeds are imbedded, either in its very substance, or in the disk of some appropriate receptacle.
5. Fungi. Mushrooms, destitute of herbage, bearing their fructification in a fleshy substance.
Such are the principles of the Linnæan Classes and Orders, which have the advantage of all other systems in facility, if not conformity to the arrangement of nature; the latter merit they do not claim. They are happily founded on two organs, not only essential to a plant, but both necessarily present at the same time; for though the Orders of the 14th and 15th Classes are distinguished by the fruit, they can be clearly ascertained even in the earliest state of the germen[1]. Tournefort founded his Orders on the fruit; and his countryman Adanson is charmed with the propriety of this measure, because the fruit comes after the flower and thus precedence is given to the nobler part which distinguishes the primary divisions or Classes! But happily the laws of a drawing-room do not extend to philosophy, and we are allowed to prefer parts which we are sure to meet with at one and the same moment, without waiting a month or two, after we have made out the Class of a plant, before we can settle its Order.
The Linnæan System, however, like all human inventions, has its imperfections and difficulties. If we meet in gardens with double or monstrous flowers, whose essential organs of fructification are deformed, multiplied, or changed to petals; or if we find a solitary barren or fertile blossom only; we must be at a loss, and in such cases could only guess at a new plant from its natural resemblance to some known one. But the principal imperfection of the System in question consists, not merely in what arises from variations in number or structure among the parts of a flower, against which no system could provide, but in the differences which sometimes occur between the number of Stamens, Styles, &c., in different plants of the same natural genus. Thus, some species of Cerastium have only 4, others 5, Stamens, though the greater part have 10. Lychnis dioica has the Stamens on one plant, the Pistils on another, though the rest of the genus has them united in the same flower; and there are several similar instances; for number in the parts of fructification is no more invariable than other characters, and even more uncertain than such as are founded on insertion, or the connexion of one part with another. Against these inconveniences the author of this System has provided an all-sufficient remedy. At the head of every Class and Order, after the genera which properly belong to them, he enumerates, in italics, all the anomalous species of genera stationed in other places, that, by their own peculiar number of Stamens or Styles, should belong to the Class or Order in question, but which are thus easily found with their brethren by means of the index.
It is further to be observed that Linnæus, ever aware of the importance of keeping the natural affinities of plants in view, has in each of his artificial Orders, and sections of those Orders, arranged the genera according to those affinities; while at the head of each Class, in his Systema Vegetabilium, he places the same genera according to their technical characters; thus combining, as far as art can keep pace with nature, the merits of a natural and an artificial system. His editors have seldom been aware of this; and Murray especially, in his 14th edition of the book just mentioned, has inserted new plants without any regard to this original plan of the work.
From the foregoing remarks it is easy to comprehend what is the real and highly important use of the Genera Plantarum of Jussieu arranged in Natural Orders, the most learned botanical work that has appeared since the Species Plantarum of Linnæus, and the most useful to those who study the philosophy of botanical arrangement. The aim of this excellent author is to bring the genera of plants together as much as possible according to their natural affinities; contructing his Classes and Orders rather from an enlarged and general view of those affinities, than from technical characters previously assumed for each Class or Order; except great and primary divisions, derived chiefly from the Cotyledons, the Petals, and the insertion of the Stamens. But his characters are so far from absolute, that at the end of almost every Order we find a number of genera merely related to it, and not properly belonging to it, and at the end of the system a very large assemblage of genera incapable of being referred to any Order whatever. Nor could a learner possibly use this system as a dictionary, so as to find out any unknown plant. The characters of the Orders are necessarily, in proportion as those Orders are natural, so widely and loosely constructed, that a student has no where to fix; and in proportion as they are here and there more defined, this, or any other system, becomes artificial, and liable to the more exceptions. The way therefore to use this valuable work, so as to ascertain an unknown plant, is, after turning to the Order or Genus to which we conceive it most probably allied, to read and study the characters and observations there brought together, as well as all to which they may allude. We shall find we learn more from the doubts and queries of Jussieu than from the assertions of most other writers. We shall readily perceive whether our plant be known to him or not; and if at the same time we refer it, by its artificial characters, to the Linnæan System, we can hardly fail to ascertain, even under the most difficult circumstances, whether it be described by either of these authors. A student may acquire a competent knowledge of natural orders, with very great pleasure to himself, by repeatedly turning over the work of Jussieu with any known plants in his hand, and contemplating their essential generic characters in the first place, and then what regards their habit and affinities; proceeding afterwards to combine in his own mind their several points of agreement, till he is competent to form an idea of those assemblages which constitute natural Classes and Orders. This will gradually extend his ideas; whereas a contrary mode would only contract them, and his Jussieu would prove merely an artificial guide, without the advantages of facility or perspicuity.
- ↑ An instance apparently to the contrary occurs in the history of my Hastingia coccinea, Exot. Bot. t. 80, a plant most evidently, both by character and natural affinity, belonging to the Didynamia Gymnospermia, but as I could no where find it described in that Order, I concluded it to be unpublished; and was not a little surprised to be told some time afterwards, that it was extant in the works of my friends Retzius and Willdenow, under Didynamia Angiospermia, by the name of Holmskioldia, after a meritorious botanist. This last name therefore, however unutterable, must remain; and I wish the Linnæan system, as well as myself, might be as free from blame in all other cases as in this.