§ II.—CHAPTER VI.

SPECIAL ORGANIC PHENOMENA VEGETABLE.

IN entering on the wide and diversified field of organic contrivance, our sole difficulty is that of selection. So crowded is it with illustrations fitted to our subject, that volumes might easily be devoted to special sections of it; and in fact, there is no other department of our evidence that has received such ample and varied, and, we may add, such skilful treatment. The work of Paley alone has made all familiar with its interesting details; and, conceived as this work is throughout in so fine a vein of homely English sense; rich with the light of a meaning everywhere clear and impressive, if not highly consecutive or profound; written, moreover, with such inimitable grace and felicity of style, it seems as if it were at once presumptuous and useless for us to enter upon ground which he has traversed with such fascinating success.⁶⁸⁶⁸   The Natural Theology, and in fact the general works of Paley, have of late somewhat lost the distinction they once enjoyed. This is undoubtedly owing to their marked deficiency in philosophic depth and comprehension, which leaves the reader so often unsatisfied, while yet pleased with their admirable clearness and sense. With an exquisite tact and homely intellect unrivalled, Paley was certainly no philosopher; and it is needless now to urge his claims in this respect. What he saw, he saw with a precision, and could express with a force and lucidity unsurpassed by any writer; but, for the most part, he not only did not see far into the deeper bearings of his subject, but there does not seem to have been any desire in his mind to do so. It will not, however, be a good sign of British thought if the works of Paley ever come to be generally depreciated. Types as they are of that healthy sobriety, tolerant temper, and quiet unobtrusive piety, which have hitherto distinguished the highest products of British theology—characteristics which, in the present day, we may well pray God it may not lose—their study can never fail to be highly advantageous to the Christian student, and to reward him with an increase of strength and manliness.138We are only led to do so from a conviction of the too obvious gap and imperfection which would otherwise be left in the course of our illustrative evidence. The knowledge of what has been already so fully accomplished in this department, will at the same time lead us to dwell upon it as briefly as we can, consistently with the necessities of our plan.

The two great characteristics of organic phenomena, in their lowest forms, we have, in the last chapter, pointed out to be assimilation and reproduction. The plant, down to its least developed specimen, exhibits these properties in contradistinction to any specimen of inorganic matter. Organisation analysed to its finest point—the minute cell, which it requires the highest powers of the microscope to detect—is marked by a forming power, quite distinct from anything in the inorganic creation. While the inorganic, at the highest point of development, is, as it has been said, a mere carrier of force, the organic is essentially a centre of force.

It is deserving of notice how complete is the structure which the microscope reveals in the elementary cell. Beaching to the rudimentary source of organisation—the hidden workshop, may we call it?—of the beautiful forms of life 139that teem all around, we are here, as everywhere, in the presence of order. The forming hand appears in the most signal manner, although we cannot trace its action, save by the delicate scrutiny of the microscope.

The general process of assimilation or nutrition in plants is of a highly interesting description. The various organs concerned in the process—the root, the stem, and the leaves—are all so many structures of the most exquisite delicacy and beauty, furnishing, in their study, a continued illustration of the Divine wisdom. We cannot now, however, dwell upon the simple construction of these organs. Their functions, in the discharge of the nutritive process, are for our object even more interesting; and to the consideration of these, therefore, we readily pass.

The root at once gives stability to the plant in the soil, and, by the fibrils which it sends forth in all directions, collects materials for its food. For this latter purpose, the fibril roots, with the main root itself (caudex), are provided with soft porous terminations, called spongioles, from their peculiar efficacy in imbibing the surrounding moisture. When the moisture, holding different matters in solution, has been absorbed, it ascends through the stem—by modes which vary, and which are not yet in all respects thoroughly understood—to the leaves, where it is partly exhaled, and partly undergoes an important chemical change, rendering it fit for becoming assimilated. The leaves are the peculiar seat of what has been called vegetable digestion, though the entire process of this, and even the nature of the action 140of the leaves, are still involved in considerable obscurity. It is certain, however, that during the day, and pre-eminently during bright sunshine, they are ceaselessly inhaling from the atmosphere carbonic acid, decomposing it, appropriating and assimilating its carbon, and exhaling its oxygen. It is, indeed, believed that during darkness this process is inverted; that oxygen is absorbed, and combined with waste or superfluous carbon, and carbonic acid exhaled; but still we know with certainty, from its own continued increment, that the plant appropriates more carbon than it rejects; that it therefore removes from the atmosphere more carbonic acid than it throws out into it; and thus that the permanent influence of these changes upon the atmosphere is in the highest degree favourable, the assimilating functions operating much more powerfully to purify than the respiratory to vitiate it. Plants are thus, in contradistinction to animals, the great conservators of atmospheric purity.

The sap, strengthened and enriched in the laboratory of the leaves, is sent back from them to the various parts of the plant for assimilation, for which it has now become exactly fitted. The same degree of uncertainty prevails regarding the precise character of the sap’s descent as exists regarding its ascent. In dicotyledonous plants its main current is through the liber, or inner portion of the bark, but it also descends through the alburnum or most recently formed wood, through which, in the same plants, flows the main current of the ascending sap. In monocotyledonous plants its passage is through the innermost layer of 141the structure, which is also the most recently formed.⁶⁹⁶⁹   It may be necessary to explain for some readers the general classification of plants into three great divisions—viz., Dicotyledons, Monocotyledons, and Acotyledons, the name being derived from the structure of the seed in the first two cases, which, in the plants of the first division, is composed of two cotyledons, or lobes enclosing the germ, or proper seed; and in plants of the second division, is composed of only one such cotyledon. Plants of the third division, such as ferns, mosses, and lichens, have no seeds properly so called, and hence, as their name imparts, no cotyledons. They are propagated by minute granular bodies called sporules, which are really nothing else than distinct plants, disjoined from the parents, and increasing by the simple addition of cellular tissue. The first and second classes are also respectively called Exogenous and Endogenous, from the peculiar formation of the stem in each case—its increase in the first class proceeding from external additions, in the second from internal development. New matter in the one case is formed by successive layers on the outside, in the other by successive layers on the inside, or towards the centre. The sap in its descent deposits the materials of fresh growth in the plant, as well as of the different well-known products,—gum, sugar, oils, and resin, so useful in domestic economy and in the arts. At the root, whence the nutritive process started, it terminates with imparting hardness and tenacity to the fibrils, and bringing matter to form new spongioles, while the old are gradually covered with an impervious cuticle.

It is impossible to contemplate this process without being impressed with its marvellous fitness and beauty. What a busy scene of orderly activity is thus every plant around us, from the noble forest-tree to the lowly lichen. And when we contemplate all the successive and intervolved adaptation conducing to the result, and again how the life, which is the result, alone gives impulse and continuance to the whole, we cannot, surely, doubt the Wisdom which 142directs and controls so finely adjusted a series of phenomena.

The phenomena of vegetable reproduction are even more strikingly manifestive of creative design. Passing by the simpler facts displayed by the cryptogamous vegetation, we have in the reproductive organs of the higher classes of plants some very curious and complicated adaptations.

These organs are all embraced in what is botanically called the flower. Its parts consist of four series or whorls, as they are technically termed—1, the calyx; 2, the corolla; 3, the stamen; 4, the pistil. These are all now regarded as merely transformations of leaves, altered so as to suit the particular functions which each performs. They sometimes appear in the form of true leaves, without any marked modification. The calyx is the outer covering of the flower—the symmetrical cup in which it commonly rests. It is usually of the same green colour as the leaves, but sometimes also, as in the fuchsia and Indian cress, it is differently coloured. Its several parts are termed sepals. The corolla is the flower, popularly so called; its parts, which are sometimes distinct and sometimes united in various ways, are termed petals. “The petals are composed of a congeries of minute cells, each containing colouring matter and delicate spirals interspersed, all being covered by a thin epidermal coat or skin. The coloured cells are distinct from one another, and thus a dark colour may be at one part and a light colour at another. How exquisitely are the colours of 143flowers diversified, and with what a masterly skill are their varied hues arranged! Whether blended or separated, as Thornton remarks, they are evidently under the control of a taste which never falls short of the perfection of elegance.”⁷⁰⁷⁰   BALFOUR’S Botanical Sketches, p. 148.

The two latter or inner organs, upon which the production of seed essentially depends, show a peculiarly minute and delicate structure. The pistil consists of a hollow tube called the style, terminating at one end in a kind of spongiole named the stigma; at the other, in the seed-vessel or ovary. The stamens, which commonly, as in the rose, enclose the pistil, consist of a stalk or filament supporting a rounded oblong body called the anther, the cells of which are filled with the fine fecundating powder termed pollen, which is sometimes little more than visible to common inspection, but presents, under the microscope, multiplied distinct forms.

There is a singular and highly interesting numerical order found to characterise the relation of all these different organs of the plant to one another. “Thus, if a flower has 5 parts of the calyx, it has usually 5 of the corolla alternating with them, 5, 10, 20, &c., stamens, and 5, or some multiple of 5, in the parts of the pistil.” And equally so when the parts of the calyx are 3 the numerical bases of 3 and 5 being the most generally prevailing in the vegetable kingdom, although the numbers 2 and 4, with their multiples, are also to be found. “It 144 is worthy of notice,” adds the author from whom we borrow these facts, “that flowers exhibiting 5 or 4, or multiples of these numbers, in their whorls, usually belong to plants having two seed-lobes or cotyledons, and which, when they form permanent woody stems, exhibit distinct zones or circles, and have separable bark; while flowers having 3, or a multiple of 3 in their whorls, present only one seed-lobe, and when they form permanent woody stems, exhibit no distinct zones nor circles, and have no separable bark. The numbers 2 and 4, or multiples of them, are seen also in the parts of fructification of flowerless plants which have no seed-lobes, such as ferns, mosses, seaweeds, &c. The processes which project from the urn-like cases of mosses are arranged in the series 4, 8, 12, 16, 32, 64, &c. The parts of fructification of scale-mosses (Jungermanniæ) are in fours, as also the germs of some sea-weeds. Thus the numbers 5 and 4 and their multiples prevail among dicotyledonous and exogenous plants; the number 3 and its multiples occur among monocotyledonous or endogenous plants; while 2 and 4, and multiples of them, are met with among acotyledonous or acrogenous plants.”⁷¹⁷¹   BALFOUR’S Sketches, pp. 137, 138.

The theistic conclusion undoubtedly receives confirmation from these and all other evidences of exact numerical relations in nature. They express very clearly the Divine plan everywhere stamped on it.

Let us now mark the reproductive process as subserved by these organs. Fecundation is the immediate result of 145communication between the stamens and pistil,—the former, which produce the pollen, being the active or male, the latter the receptive or female organs. In the great majority of cases the stamens and pistil are found on the same plant, the former overtopping the latter—an arrangement which gives the most simple mode of fecundation, by enabling the stigma readily to receive the falling pollen as it bursts from the anther. In order to secure this purpose more effectually, the stigma exudes a slightly glutinous fluid, to which the grains of the pollen adhere. These grains, whose manifold structure, as seen under the microscope, has been already noticed, have each two coats, one of which bursts when the grain is ripe, and the other, in touching the stigma, elongates itself into the shape of a slender tube, passing downwards through the style into the ovary, and so conveying to the germ the vivifying fluid. “The cells of the stigma are beautifully contrived to admit the passage of these tubes, as they are long, and extremely loose in texture, at the same time so moist and elastic as to be easily compressed when necessary. It is so contrived that the minute particles contained in the grains enter slowly to the ovary, as it seems necessary that the fecundating matter should be admitted by degrees. It is also necessary that the tube should enter the foramen of the ovule; and as the ovule is not always in a proper position to receive it, it will be found to erect itself or to turn, as the case may be, while the granules of the pollen grains are passing down the tubes.”⁷²⁷²   Vegetable Physiology, p. 79. Edinburgh: Chambers.

In drooping flowers, such as the fuchsia—where it would be obviously no longer fitting that the stamens should exceed the pistil in length, as thereby the pollen would be scattered on the ground instead of reaching the stigma—the relation of the parts is found inverted in correspondence with the altered character of the plant. And, in fact, nothing can be more beautiful and impressive than the great variety of adaptations by which, in special cases, communication is secured between the pollen and the pistils. “In the common nettle the stamens have elastic filaments, which are at first bent down, so as to be obscured by the calyx; but when the pollen is ripe, the filaments jerk out, and thus scatter the powder on the pistils, which occupy separate flowers. In the common barberry, the lower part of the filament is very irritable; and whenever it is touched, the stamen moves forward to the pistil. In the style-wort (Stylidium) the stamens and pistil are united in a common column which projects from the flower; this column is very irritable at the angle where it leaves the flower, and when touched, it passes with a sudden jerk from one side to the other, and thus scatters the pollen. In the hazel, where the pollen is in one set of flowers and the pistil in another, the leaves might interfere with the application of the pollen, and therefore they are not produced until it has been scattered.”⁷³⁷³   BALFOUR’S Sketches, p. 152-154. In Diœcious plants, such as the willow, where the flowers are not only unisexual, but the stamen-bearing are on one tree and the pistil-bearing on another, the process 147 of communication is effected in some cases by the winds, but in other cases, after a more complicated and ingenious manner, by insects. The bee, while providing food for its young, is at the same time aiding in the dispersion of the pollen. The peculiar shape of some flowers—the Orchids especially—seems to form an attraction for certain insects which are helpful in the same office. One of the most remarkable examples of this insect-agency in the distribution of the pollen is furnished by the birthwort (Aristolochia). In this plant the “flower consists of a long tube in a chamber, at the bottom of which the stamens and pistil are placed, completely shut out from the agency of the winds. It is frequented, in its native country, by an insect which enters the tube easily, and gets into the little chamber. On attempting to get out, it is prevented by a series of hairs in the tube, which all point downwards. It therefore moves about in the little cavity, and thus distributes the pollen on the pistil, soon after which the flower withers and the insect escapes.”⁷⁴⁷⁴   BALFOUR’S Sketches, p. 158-159.

When impregnation is completed, the other parts of the flower decay, whilst the “gravid seed-vessel” increases in bulk, till it becomes, under very diversified forms, what is called the fruit. All these forms, many of which are so familiarly known and useful, would seem to have one prime object in view, viz. the preservation of the seed. The production of this seed has been the great end of the process hitherto described; and, this end accomplished, the flower dies, whilst the energies of the plant are turned to the nursing 148of the little embryo which it has left behind, and which is destined in its time to advance into new forms of floral beauty. “Nothing,” adds Paley,⁷⁵⁷⁵   Natural Theology, Knight’s edit., vol. iii. p. 58. “can be more single than the design, more diversified than the means. Pellicles, shells, pulps, pods, husks, skin, scales armed with horns, are all employed in prosecuting the same intention.”

When the seeds reach maturity, their dispersion is provided for in various interesting ways. In some cases the fruit falls without opening, and gradually decays, forming a sort of manure with the soil in which the plant sprouts. In other cases the seed-vessels open and scatter the seeds. “In the common broom, the pod, when ripe, opens with considerable force; so also the fruit of the sandbox-tree, and the balsam, which is called Touch-me-not, on account of its seed-vessel bursting when touched. The squirting cucumber, when handled in its ripe state, gives way at the point where the fruit joins the stalk, and the seeds are sent out with amazing force. The common geranium seed-vessels curl up when ripe, and scatter the seeds. In the case of firs, bignonias, and some other plants, the seeds are furnished with winged appendages; while in the cotton-plant and asclepias they have hairs attached to them, by means of which they are wafted to a distance.” “The plant called Rose of Jericho becomes dried up like a ball, and is tossed about by the wind until it comes into contact with water, when its small pods open, and the seeds are scattered; and a species of fig-marigold in Africa opens its seed-vessel when moisture is 149 applied.” “In the dandelion, the leaves which surround the clusters or heads of flowers are turned downwards, the receptacle becomes convex and dry, the hairs spread out so as to form a parachute-like appendage to each fruit, and collectively to present the appearance of a ball, and in this way the fruit is prepared for being dispersed by the winds.”⁷⁶⁷⁶   BALFOUR’S Sketches, pp. 44, 172, 173, 174.

The seed being deposited in the soil, the process of germination takes place under the influence of heat, air, and moisture. The embryo sends forth, in one direction, a number of fibrous threads, which fix the plant in the ground. The radicle, in short, becomes the root. The plumule on the other side elongates itself, rising into the air in the form of the stem, frequently accompanied by one or more cotyledons or seed-leaves, according to the nature of the plant.

And thus the great processes of nutrition and reproduction again proceed in the same varied and beautiful round, proclaiming the Wisdom which guides and which guards the whole.

We might add indefinitely to the force of these illustrations, by a consideration of the same processes as exemplified in the animal kingdom. In this field we might easily glean some examples of peculiarly elaborate and striking contrivance,⁷⁷⁷⁷   The suckling the kangaroo, admirably described by Dr Whewell (Indications of the Creator, p. 123-124), is among the most remarkable of such instances for complication, and at the same time propriety, of contrivance. subservient to the production and preservation of those higher and more complex forms of life which here meet us. The numerous and intricate organs employed in digestion, 150 in the circulation of the blood, in respiration, and the exquisite order and regularity with which they perform their functions, are especially marked with instructive meaning in reference to our subject. As, however, according to our whole plan, we do not and cannot aim at a mere accumulation of instances which do not add some significance to our evidence, we pass onwards to those higher illustrations presented by the muscular and nervous phenomena, which are considered to be the distinctive characteristics of the animal kingdom.