CHAPTER XVII.

PEDIGREE AND HISTORY OF THE VEGETABLE KINGDOM.

The Natural System of the Vegetable Kingdom.-Division of the Vegetable Kingdom into Six Branches and Eighteen Cla.s.ses.-The Flowerless Plants (Cryptogamia).-Sub-kingdom of the Thallus Plants.-The Tangles, or Algae (Primary Algae, Green Algae, Brown Algae, Red Algae).-The Thread-plants, or Inophytes (Lichens and Fungi).-Sub-kingdom of the Prothallus Plants.-The Mosses, or Muscinae (Water-mosses, Liverworts, Leaf-mosses, Bog-mosses).-The Ferns, or Filicinae (Leaf-ferns, Bamboo-ferns, Water-ferns, Scale-ferns).-Sub-kingdom of Flowering Plants (Phanerogamia).-The Gymnosperms, or Plants with Naked Seeds (Palm-ferns = Cycadeae; Pines = Coniferae).-The Angiosperms, or Plants with Enclosed Seeds.-Monocotylae.-Dicotylae.-Cup-blossoms (Apetalae).-Star-blossoms (Diapetalae).-Bell-blossoms (Gamopetalae).

Every attempt that we make to gain a knowledge of the pedigree of any small or large group of organisms related by blood must, in the first instance, start with the evidence afforded by the existing "_natural system_" of this group. For although the natural system of animals and plants will never become finally settled, but will always represent a merely approximate knowledge of true blood relationship, still it will always possess great importance as a hypothetical pedigree. It is true, by a "natural system" most zoologists and botanists only endeavour to express in a concise way the subjective conceptions which each has formed of the objective "_form-relationships_" of organisms. These form-relationships, however, as the reader has seen, are in reality the necessary result of true _blood relationship_. Consequently, every morphologist in promoting our knowledge of the natural system, at the same time promotes our knowledge of the pedigree, whether he wishes it or not. The more the natural system deserves its name, and the more firmly it is established upon the concordance of results obtained from the study of comparative anatomy, ontogeny, and palaeontology, the more surely may we consider it as the approximate expression of the true pedigree of the organic world.

In entering upon the task contemplated in this chapter, the genealogy of the vegetable kingdom, we shall have, according to this principle, first to glance at the _natural system of the vegetable kingdom_ as it is at present (with more or less important modifications) adopted by most botanists. According to the system generally in vogue, the whole series of vegetable forms is divided into two main groups. These main divisions, or sub-kingdoms, are the same as were distinguished more than a century ago by Charles Linnaeus, the founder of systematic natural history, and which he called _Cryptogamia_, or secretly-blossoming plants, and _Phanerogamia_, or openly-flowering plants. The latter, Linnaeus, in his artificial system of plants, divided, according to the different number, formation, and combination of the anthers, and also according to the distribution of the s.e.xual organs, into twenty-three different cla.s.ses, and then added the Cryptogamia to these as the twenty-fourth and last cla.s.s.

The _Cryptogamia_, the secretly-blossoming or flowerless plants, which were formerly but little observed, have in consequence of the careful investigations of recent times been proved to present such a great variety of forms, and such a marked difference in their coa.r.s.er and finer structure, that we must distinguish no less than fourteen different cla.s.ses of them; whereas the number of cla.s.ses of flowering plants, or _Phanerogamia_, may be limited to four. However, these _eighteen cla.s.ses of the vegetable kingdom_ can again be naturally grouped in such a manner that we are able to distinguish in all _six main divisions_ or _branches_ of the vegetable kingdom. Two of these six branches belong to the flowering, and four to the flowerless plants. The table on page 82 shows how the eighteen cla.s.ses are distributed among the six branches, and how these again fall under the _sub-kingdoms_ of the vegetable kingdom.

The one sub-kingdom of the _Cryptogamia_ may now be naturally divided into _two_ divisions, or sub-kingdoms, differing very essentially in their internal structure and in their external form, namely, the Thallus plants and the Prothallus plants. The group of _Thallus plants_ comprises the two large branches of Tangles, or Algae, which live in water, and the Thread-plants, or Inophytes (Lichens and Fungi), which grow on land, upon stones, bark of trees, upon decaying bodies, etc. The group of _Prothallus plants_, on the other hand, comprises the two branches of Mosses and Ferns, containing a great variety of forms.

All _Thallus plants, or Thallophytes_, can be directly recognized from the fact that the two morphological fundamental organs of all other plants, stem and leaves, cannot be distinguished in their structure. The complete body of all Algae and of all Thread-plants is a ma.s.s composed of simple cells, which is called a _lobe_, or _thallus_. This thallus is as yet not differentiated into axial-organs (stem and root) and leaf-organs. On this account, as well as through many other peculiarities, the Thallophytes contrast strongly with all remaining plants-those comprised under the two sub-kingdoms of Prothallus plants and Flowering plants-and for this reason the two latter sub-kingdoms are frequently cla.s.sed together under the name of _Stemmed plants_, or _Cormophytes_. The following table will explain the relation of these three sub-kingdoms to one another according to the two different views:-

{ A. Thallus Plants } I. Thallus Plants { (_Thallophyta_) } (_Thallophyta_) I. Flowerless Plants. { (_Cryptogamia_) { { B. Prothallus Plants } { (_Prothallophyta_) } } II. Stemmed Plants } (_Cormophyta_) } II. Flowering Plants { C. Flowering Plants } (_Phanerogamia_) { (_Phanerogamia_) }

The stemmed plants, or Cormophytes, in the organization of which the difference of axial-organs (stem and root) and leaf-organs is already developed, form at present, and have, indeed, for a very long period formed, the princ.i.p.al portion of the vegetable world. However, this was not always the case. In fact, stemmed plants, not only of the flowering group, but even of the prothallus group, did not exist at all during that immeasurably long s.p.a.ce of time which forms the beginning of the first great division of the organic history of the earth, under the name of the archilithic, or primordial period. The reader will recollect that during this period the Laurentian, Cambrian, and Silurian systems of strata were deposited, the thickness of which, taken as a whole, amounts to about 70,000 feet. Now, as the thickness of all the more recent super-inc.u.mbent strata, from the Devonian to the deposits of the present time, taken together, amounts to only about 60,000 feet, we were enabled from this fact alone to draw the conclusion-which is probable also for other reasons-that the archilithic, or primordial, period was of longer duration than the whole succeeding period down to the present time. During the whole of this immeasurable s.p.a.ce of time, which probably comprises many millions of centuries, vegetable life on our earth seems to have been represented exclusively by the sub-kingdom of Thallus plants, and, moreover, only by the cla.s.s of marine Thallus plants, that is to say, the Algae. At least all the petrified remains which are positively known to be of the primordial period belong exclusively to this cla.s.s. As all the animal remains of this immense period also belong exclusively to animals that lived in water, we come to the conclusion that at that time organisms adapted to a life on land did not exist at all.

For these reasons the first and most imperfect of the great provinces or branches of the vegetable kingdom, the division of the Algae, or Tangles, must be of special interest to us. But, in addition, there is the interest which this group offers when viewed by itself. In spite of the exceedingly simple composition of their const.i.tuent cells, which are but little differentiated, the Algae show an extraordinary variety of different forms. To them belong the simplest and most imperfect of all forms, as well as very highly developed and peculiar forms. The different groups of Algae are distinguished as much by size of body as by the perfection and variety of their outer form. At the lowest stage we find such species as the minute Protococcus, several hundred thousands of which occupy a s.p.a.ce no larger than a pin's head. At the highest stage we marvel at the gigantic Macrocysts, which attain a length of from 300 to 400 feet, the longest of all forms in the vegetable kingdom.

It is possible that a large portion of the coal has been formed out of Algae. If not for these reasons, yet the Algae must excite our special attention from the fact that they form the beginning of vegetable life, and contain the original forms of all other groups of plants, supposing that our monophyletic hypothesis of a common origin for all groups of plants is correct. (Compare p. 83.)

SYSTEMATIC VIEW

_Of the Six Branches and Eighteen Cla.s.ses of the Vegetable Kingdom._

========================================================================================== _Primary Groups_ | | | _or Sub-Kingdoms_ | _Branches or Clades_ | _Cla.s.ses_ | _Systematic Name_ _of the_ | _of the_ | _of the_ | _of the_ _Vegetable Kingdom._ | _Vegetable Kingdom._ | _Vegetable Kingdom._ | _Cla.s.ses._ ------------------------+-----------------------+----------------------+------------------

{ { 1. Primaeval algae 1. _Archephyceae_ { { (Protophyta) { { { I. { 2. Green algae 2. _Chlorophyceae_ A. { Tangles { (Chloroalgae) =Thallus Plants= { _Algae_ { Thallophyta { { 3. Brown algae 3. _Phaeophyceae_ { { (Fucoideae) { { { { 4. Red algae 4. _Rhodophyceae_ { { (Florideae)

{ II. { 5. Lichens 5. _Lichenes_ { Thread-plants { { _Inophyta_ { 6. Fungi 6. _Fungi_ { { { 7. Tangle-mosses 7. _Charobrya_ { { (Characeae) { { { III. { 8. Liverworts 8. _Thallobrya_ { Mosses { (Hepaticae) { _Muscinae_ { { { 9. Frondose-mosses 9. _Phyllobrya_ B. { { (Frondosae) =Prothallus= { { =Plants= { { 10. Turf-mosses 10. _Sphagn.o.brya_ Prothallophyta { (Sphagnaceae) { { { 11. Shaft-ferns 11. _Calamariae_ { { (Calamophyta) { IV. { { Ferns { 12. Frondose-ferns 12. _Filices_ { _Felicinae_ { (Pterideae) { { { { 13. Aquatic ferns 13. _Rhizocarpeae_ { { (Hydropterides) { { { { 14. Scale-ferns 14. _Selagineae_ { { (Lepidophyta)

{ V. { { Plants with { 15. Palm-ferns 15. _Cycadeae_ C. { Naked Seeds { =Flowering Plants= { _Gymnosperma_ { 16. Pines 16. _Coniferae_ Phanerogamia { { VI. { 17. Plants with 17. _Monocotylae_ { Plants with { one seed lobe { Enclosed Seeds { { _Angiosperma_ { 18. Plants with 18. _Dicotylae_ { { two seed lobes

_Gamopetalae_ (Flowers with corolla) | _Dialypetalae_ (Star-shaped flowers) | _Monochlamydeae_ MONOCOTYLEDONae (Flowers with calyx) (One seed-lobed plants) | | DICOTYLEDONae | (Two seed-lobed plants) | | | --------------------v-------------/ CONIFERae +Angiospermae+ CYCADEae (Pines) (Plants with enclosed seeds) (Palm-ferns) | GNETACEae | | | | | -----------v-----------------------/ +Gymnospermae+ (Plants with naked seeds) _Phanerogamae_ | (Flowering plants) _Pterideae_ _Selagineae_ | _Rhizocarpeae_ | (Frondose-ferns) (Scaled-ferns) |(Water-ferns) | | _Calamariae_ | | | | | (Shaft-ferns) | | | | | | -------------------------------v------------------------/ +Filicinae+ _Frondosae_ _Sphagnaceae_ (Ferns) (Leaf-mosses) (Turf-mosses) | | | | CHARACEae ----------------v------------/ (Tangle-mosses) | | _Hepaticae_ (Liverworts) | | | ------------------v--------------------/ +Muscinae+ (Mosses) _Fucoideae_ | _Florideae_ (Brown Algae) | _Lichenes_ (Red Algae) | _Chlorophyceae_ (Lichens) | | (Green Algae) | | | | | ------------------v-----------------/ +Fungi Inophyta+ +Algae+ (Tangles) (Thread-plants) | | -------v------------------------------/ _Protophyta_ (Primaeval Plants) | _Vegetable Monera_

Most people living inland can form but a very imperfect idea of this exceedingly interesting branch of the vegetable kingdom, because they know only its proportionately small and simple representatives living in fresh water. The slimy green aquatic filaments and flakes of our pools and ditches and springs, the light green slimy coverings of all kinds of wood which have for any length of time been in contact with water, the yellowish green, frothy, and oozy growths of our village ponds, the green filaments resembling tufts of hair which occur everywhere in fresh water, stagnant and flowing, are for the most part composed of different species of Algae. Only those who have visited the sea-sh.o.r.e, and wondered at the immense ma.s.ses of cast-up seaweed, and who, from the rocky coast of the Mediterranean, have seen through the clear blue waters the beautifully-formed and highly-coloured vegetation of Algae at the bottom, know how to estimate the importance of the cla.s.s of Algae. And yet, even these marine Algae-forests of European sh.o.r.es, so rich in forms, give only a faint idea of the colossal forests of Sarga.s.so in the Atlantic ocean, those immense banks of Algae, covering a s.p.a.ce of about 40,000 square miles-the same which made Columbus, on his voyage of discovery, believe that a continent was near. Similar but far more extensive forests of Algae grew in the primaeval ocean, probably in dense ma.s.ses, and what countless generations of these archilithic Algae have died out one after another is attested, among other facts, by the vast thickness of Silurian alum schists in Sweden, the peculiar composition of which proceeds from those ma.s.ses of submarine Algae. According to the recently expressed opinion of Frederick Mohr, a geologist of Bonn, even the greater part of our coal seams have arisen out of the acc.u.mulated dead bodies of the Algae forests of the ocean.

Within the branch of the Algae we distinguish four different cla.s.ses, each of which is again divided into several orders and families. These again contain a large number of different genera and species. We designate these four cla.s.ses as Primaeval Algae, or Archephyceae, Green Algae, or Chlorophyceae, Brown Algae, or Phaeophyceae, and Red Algae, or Rhodophyceae.

The first cla.s.s of Algae, the _Primaeval_ Algae (Archephyceae), might also be called _primaeval plants_, because they contain the simplest and most imperfect of all plants, and, among them, those most ancient of all vegetable organisms out of which all other plants have originated. To them therefore belong those most ancient of all vegetable Monera which arose by spontaneous generation in the beginning of the Laurentian period. Further, we have to reckon among them all those vegetable forms of the simplest organization which first developed out of the Monera in the Laurentian period, and which possessed the form of a single plastid. At first the entire body of one of these small primary plants consisted only of a most simple cytod (a plastid without kernel), and afterwards attained the higher form of a simple cell, by the separation of a kernel in the plasma. (Compare above, vol. i. p. 345.) Even at the present day there exist various most simple forms of Algae which have deviated but little from the original primary plants. Among them are the Algae of the families Codiolaceae, Protococcaceae, Desmidiaceae, Palmellaceae, Hydrodictyeae, and several others. The remarkable group of Phycochromaceae (Chroococcaceae and Oscillarineae) might also be comprised among them, unless we prefer to consider them as an independent tribe of the kingdom Protista.

The monoplastic Protophyta-that is, those primary Algae formed by a single plastid-are of the greatest interest, because the vegetable organism in this case completes its whole course of life as a perfectly simple "individual of the first order," either as a cytod without kernel, or as a cell containing a kernel.

Among the primary plants consisting of a single cytod are the exceedingly remarkable Siphoneae, which are of considerable size, and strangely "mimic" the forms of higher plants. Many of the Siphoneae attain a size of several feet, and resemble an elegant moss (Bryopsis), or in some cases a perfect flowering plant with stalks, roots, and leaves (Caulerpa) (Fig. 17). Yet the whole of this large body, externally so variously differentiated, consists internally of an entirely simple sack, possessing the negative characters of a simple cytod.

[Ill.u.s.tration: FIG. 17.-Caulerpa denticulata, a monoplastic Siphonean _of the natural size_. The entire branching primary plant, which appears to consist of a creeping stalk with fibrous roots and indented leaves, is in reality only _a single plastid_, and moreover a cytod (without a kernel), not even attaining the grade of a cell with nucleus.]

These curious Siphoneae, Vaucheriae, and Caulerpae show us to how great a degree of elaboration a single cytod, although a most simple individual of the first order, can develop by continuous adaptation to the relations of the outer world. Even the _single-celled primary plants_-which are distinguished from the monocytods by possessing a kernel-develop into a great variety of exquisite forms by adaptation; this is the case especially with the beautiful _Desmidiaceae_, of which a species of Euastrum is represented in Fig. 18 as a specimen.

[Ill.u.s.tration: FIG. 18.-Euastrum rota, a single-celled Desmid, much enlarged. The whole of the star-shaped body of this primaeval plant has the formal value of a simple cell. In its centre lies the kernel, and within this the kernel corpuscle, or speck.]

It is very probable that similar primaeval plants, the soft body of which, however, was not capable of being preserved in a fossil state, at one time peopled the Laurentian primaeval sea in great ma.s.ses and varieties, and in a great abundance of forms, without, however, going beyond the stage of individuality of a simple plastid.

The group of _Green Tangles_ (Chlorophyceae), or _Green Algae_ (Cloroalgae), are the second cla.s.s, and the most closely allied to the primaeval group. Like the majority of the Archephyceae, all the Chlorophyceae are coloured green, and by the same colouring matter-the substance called leaf-green, or chlorophyll-which colours the leaves of all the higher plants.

To this cla.s.s belong, besides a great number of low marine Algae, most of the Algae of fresh water, the common water hair-weeds, or Confervae, the green slime-b.a.l.l.s, or Glosphaerae, the bright green water-lettuce, or Ulva, which resembles a very thin and long lettuce leaf, and also numerous small microscopic algae, dense ma.s.ses of which form a light green shiny covering to all sorts of objects lying in water-wood, stones, etc.

These forms, however, rise above the simple primary Algae in the composition and differentiation of their body. As the green Algae, like the primaeval Algae, mostly possess a very soft body, they are but rarely capable of being petrified. However, it can scarcely be doubted that this cla.s.s of Algae-which was the first to develop out of the preceding one-most extensively and variously peopled the fresh and salt waters of the earth in early times.

In the third cla.s.s, that of the _Brown Tangles_ (Phaeophyceae), or _Black Algae_ (Fucoideae), the _branch_ of the Algae attains its highest stage of development, at least in regard to size and body. The characteristic colour of the Fucoid is more or less dark brown, sometimes tending more to an olive green or yellowish green, sometimes more to a brownish red or black colour.

Among these are the largest of all Algae, which are at the same time the longest of all plants, namely, the colossal giant Algae, amongst which the Macrocystis pyrifera, on the coast of California, attains a length of 400 feet. Also, among our indigenous Algae, the largest forms belong to this group. Especially I may mention here the stately sugar-tangle (Laminaria), whose slimy, olive green thallus-body, resembling gigantic leaves of from 10 to 15 feet in length, and from a half to one foot in breadth, are thrown up in great ma.s.ses on the coasts of the North and Baltic seas.

To this cla.s.s belongs also the bladder-wrack (Fucus vesiculosus) common in our seas, whose fork-shaped, deeply-cut leaves are kept floating on the water by numerous air bladders (as is the case, too, with many other brown Algae). The freely floating Sarga.s.so Alga (Sarga.s.so bacciferum), which forms the meadows or forests of the Sarga.s.so Sea, also belongs to this cla.s.s.

Although each individual of these large alga-trees is composed of many millions of cells, yet at the beginning of its existence it consists, like all higher plants, of a single cell-a simple egg. This egg-for example, in the case of our common bladder-wrack-is a naked, uncovered cell, and as such is so like the naked egg-cells of lower marine animals-for example, those of the Medusae-that they might easily be mistaken one for another (Fig. 19).

[Ill.u.s.tration: FIG. 19.-The egg of the common bladder-wrack (Fucus vesiculosus), a simple naked cell, much enlarged. In the centre of the naked globule of protoplasm the bright kernel is visible.]

It was probably the Fucoideae, or Brown Algae, which during the primordial period, to a great extent const.i.tuted the characteristic alga-forests of that immense s.p.a.ce of time. Their petrified remains, especially those of the Silurian period, which have been preserved, can, it is true, give us but a faint idea of them, because the material of these Algae, like that of most others, is ill-suited for preservation in a fossil state. As has already been remarked, a large portion of coal is perhaps composed of them.

Less important is the fourth cla.s.s of Algae, that of the _Rose-coloured Algae_ (Rhodophyceae), or _Red Sea-weeds_ (Florideae). This cla.s.s, it is true, presents a great number of different forms; but most of them are of much smaller size than the Brown Algae. Although they are inferior to the latter in perfection and differentiation, they far surpa.s.s them in some other respects. To them belong the most beautiful and elegant of all Algae, which on account of the fine plumose division of their leaf-like bodies, and also on account of their pure and delicate red colour, are among the most charming of plants. The characteristic red colour sometimes appears as a deep purple, sometimes as a glowing scarlet, sometimes as a delicate rose tint, and may verge into violet and bluish purple, or on the other hand into brown and green tints of marvellous splendour. Whoever has visited one of our sea-coast watering places, must have admired the lovely forms of the Florideae, which are frequently dried on white paper and offered for sale.

Most of the Red Algae are so delicate, that they are quite incapable of being petrified; this is the case with the splendid Ptilotes, Plocamia, Delesseria, etc. However, there are individual forms, like the Chondria and Sphaerococca, which possess a harder thallus, often almost as hard as cartilage, and of these fossil remains have been preserved-princ.i.p.ally in the Silurian, Devonian, and Carboniferous strata, and later in the oolites. It is probable that this cla.s.s also had an important share in the composition of the archilithic Algae flora.

If we now again take into consideration the flora of the primordial period, which was exclusively formed by the group of Algae, we can see that it is not improbable that its four subordinate cla.s.ses had a share in the composition of those submarine forests of the primaeval oceans, similar to that which the four types of vegetation-trees with trunks, flowering shrubs, gra.s.s, and tender leaf-ferns and mosses-at present take in the composition of our recent land forests.

We may suppose that the submarine tree forests of the primordial period were formed by the huge Brown Algae, or Fucoideae. The many-coloured flowers at the foot of these gigantic trees were represented by the gay Red Algae, or Florideae. The green gra.s.s between was formed by the hair-like bunches of Green Algae, or Chloroalgae. Finally, the tender foliage of ferns and mosses, which at present cover the ground of our forests, fill the crevices left by other plants, and even settle on the trunks of the trees, at that time probably had representatives in the moss and fern-like Siphoneae, in the Caulerpa and Bryopsis, from among the cla.s.s of the primary Algae, Protophyta, or Archephyceae.

With regard to the relationships of the different cla.s.ses of Algae to one another and to other plants, it is exceedingly probable that the Primary Algae, or Archephyceae, as already remarked, form the common root of the pedigree, not merely for the different cla.s.ses of Algae, but for the whole vegetable kingdom. On this account they may with justice be designated as primaeval plants, or Protophyta.

Out of the naked vegetable Monera, in the beginning of the Laurentian period, enclosed cytods were probably the first to arise (vol. i. p.

345), by the naked, structureless, alb.u.minous substance of the Monera becoming condensed in the form of a pellicle on the surface, or by secreting a membrane. At a later period, out of these enclosed cytods genuine vegetable cells probably arose, as a kernel or nucleus separated itself in the interior from the surrounding cell-substance or plasma.

The three cla.s.ses of Green Algae, Brown Algae, and Red Algae, are perhaps three distinct cla.s.ses, which have arisen independently of one another out of the common radical group of Primaeval Algae, and then developed themselves further (each according to its kind), and have variously branched off into orders and families. The Brown and Red Algae possess no close blood relationship to the other cla.s.ses of the vegetable kingdom.

These latter have most probably arisen out of the Primaeval Algae, either directly or by the intermediate step of the Green Algae.

It is probable that Mosses (out of which, at a later time, Ferns developed) proceeded from a group of Green Algae, and that Fungi and Lichens proceeded from a group of Primaeval Algae. The Phanerogamia developed at a much later period out of Ferns.

As a second cla.s.s of the Vegetable Kingdom we have above mentioned the _Thread-plants_ (Inophyta). We understood by this term the two closely related cla.s.ses of _Lichens_ and _Fungi_. It is possible that these Thallus plants have not arisen out of the Primaeval Algae, but out of one or more Monera, which, independently of the latter, arose by spontaneous generation. It appears conceivable that many of the lowest Fungi, as for example, many ferment-causing fungi (forms of Micrococcus, etc.), owe their origin to a number of different _archigonic_ Monera (that is, Monera originating by spontaneous generation).