Botanical letters to a friend

Letter 1. DEFINITION OF BOTANY - = Res Ae as 3 4

10. 11 12.

13, 14, 15,

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ELEMENTARY PARTS OF THE PLANT - = be GENESIS OF THE CELL - = pe a

UNION OF THE CELLS; CHANGES RESULTING FROM THEIR GROWTH

. CHEMISTRY OF THE PLANT - = a =

ABSORPTION AND DISTRIBUTION OF THE PLANT’S FOOD; SEPA- RATION OF WATER ~ - a a

. PHENOMENA OF ASSIMILATION - ~ =

CONFIGURATION OF THE PLANT, FUNDAMENTAL ORGANS - THE PLANT CONSIDERED AS A LEAVED AXIS ~ - LEAF FORMATIONS - - - - ARCHITECTURAL ARRANGEMENT OF THE PLANT. PHYLLOTAXY PROPAGATION OF THE PLANT - - - FORMATION OF SHOOTS - - - - Unity OF RACE AND OF THE HIGHER CATEGORIES - -

THE PLANT WORLD IN ITS LOCAL DISTRIBUTION. GEOGRAPHY OF PLANTS - = = = -

CHRONOLOGICAL ASPECT OF THE PLANT, HISTORY OF THE PLANT WORLD = = ~ =

NATURE OF THE PLANT, ITS POSITION IN THE SCHEME OF CREATION - - - ~ -

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BOTANICAL LETTERS.

LETTER I.

DEFINITION OF BOTANY.

ir cannot be denied that at the present day the natural sciences have acquired a prominence in the arena of intellectual activity superior to any other branches of knowledge, and that they especially characterise both the spirit and tendency of the age, as well as the direction in which it is striving to develope itself. There exists, at the same time, between these sciences a relationship so intimate; the support which they mutually afford to each other is so manifold in its nature; their transition into each other is so frequent ; and they progress with such increasing impetus; that there is, indeed, a difficulty in doubting that, thus united, they will arrive at some valuable result, sooner than has hitherto been the case, while cultivated in a different spirit.

The investigation of nature and its activity is, moreover, so elevated a field of mental exercise, that, to the healthy and unde-

* praved mind, it affords the most cotigenial and advantageous preparation for the higher intellectual occupations of life.

Although in former periods of culture the natural sciences have either been disregarded by the generality of men, or, when cultivated, were interwoven with many foreign elements, this must, probably, be regarded as a result rather of the impatience with which men strove to reach the goal of their thought and labour, than of any want of conviction that the solution of more difficult problems must give place to that of the less complicated ones.

B ay BOTANICAL LETTERS.

Nevertheless, those branches of knowledge even which are concerned with the most simple conception of nature in its material aspect, have shared the same fate as all the other natural sciences; so that it is impossible to do otherwise than admit that the former, no less than the latter, are the offspring of modern time.

In this respect, mineralogy, botany, and zodlogy, are upon precisely the same footing. Whatever they may be they have become within a very short and recent period. Since several other natural sciences have already found their representatives before the general public, I will here venture to discuss the second of those named above; to examine somewhat more closely into its present condition; and not only to show in what kind of connexion it stands to its more immediate congeners, but likewise to determine what is its position in the general range of natural science. The interest which has always been taken in the scientia amabilis will, perhaps, be a sufficient excuse for my bringing it forward—of course in its holiday attire.

When we reflect upon the spirit which animated the labours of a number of investigators, especially during the latter part of the last century, and led them to seek for some knowledge of the extent and distribution of the plant world; its rich treasure of forms ; its phenomena of vital activity ; and even of its several phases of creation ; the advance which has been made in botanical science cannot be regarded as other than satisfactory. The attainment of this happy result has been contributed to, not only by botanists, but certainly in an equal degree by physicists, chemists, geognosts, geologists, etc. New, and hitherto unthought-of, questions have not only been raised on all sides, but they have likewise either met with a satisfactory solution, or the path to it has already been struck out. The modest demands which were hitherto made upon the man skilled in the knowledge of plants have been considerably augmented; and the mere acquaintance with the coiffure, uniform, rank, and merit of the descendents of Greece’s most fruitful goddess—subjects which in the age ot Linneus constituted the corner-stone of all botanical erudition—is now, in consequence of the repeated metamorphoses of this science, either entirely put on one side, or employed only as a groundwork, and that in a very restricted sense.

The botanical science of the present day is constructed upon an entirely different plan from that of an earlier period, and, consequently, has a tendency and aim equally distinct and different.

Although the necessity for a knowledge of the names of plants remains, upon the whole, the same as hitherto, although from the constantly-increasing material, and continual discovery of new forms, the distinctions between them are unceasingly multiplied, and it is requisite that the muster-roll should be maintained in good order, still these occupations have not wholly engrossed the attention of botanists. By an appropriate division of labour, it has been rendered possible for some to consider more general questions relating to the actual nature of the things we call plants; in what consist their life and functions; what connects them with the outer world; and what may be their purpose and destiny in the great economy of nature—questions which lie far beyond the boundaries of the botany of any earlier period.

When these investigations into the nature of the plant had once been entered upon, the transition into another department of science followed as a natural consequence. But, so long as these questions were considered only in their universal form, the results arrived at did not amount to much more than abstract and questionable hypotheses; it was not until, separating the general from the special point of view, investigators turned their attention to details, and attempted to reach the solution of the general problem by the study of particular instances, that their labours were crowned with anything like success. The fortunate turn thus taken in the cultivation of botany is but of recent date, and its result is in so far certain that it bids fair to give rise to a physics of plant organism.

But how far distant we still are from this end may easily be seen by the most superficial glance at botanical literature which, with no lack of voluminous works, does not possess one which accounts for any, even of the most ordinary, phenomena of plant life ina manner at all satisfactory. All the plant treasures that

B 2 have been collected by naturalists of every clime; by travellers in the most remote corners of the world, not unfrequently at the risk or even sacrifice of their lives, and deposited in museums, botanical gardens, etc., where they have been studied and arranged with the most laborious and persevering industry ; all these can do no more than furnish the raw material for scientific investigation which has yet to be undertaken. The matter is in nowise different with regard to the experience which has been gained in the culture of plants either of one kind or the other. Neither agriculture, nor forestry, the growth of fruit, or gardening, is yet advanced beyond the most meagre empiricism, and, unfortunately, occupy time and talents which are capable of more advantageous application. But we cannot reasonably be surprised at this, as we have already admitted being in the dark with regard to the most simple operations of plant life. It is but a little while that we have known, and that only in an imperfect manner, how the plant is nourished, how it grows, increases, and propagates. There is not a single plant of whose gradual alterations in form and condition, from the commencement of its growth to the termination of its existence, we have any knowledge. In this great field of scientific discovery there is as much to be done by the botanist as by the geographer in the interior of Africa or Australia.

But while contemplating that which les before us, we will not look backwards with disdain; we will not be guilty of ineratitude to our predecessors, but congratulate ourselves on the results of their labours, however deficient they may be, bearing well in mind that it is only by means of them we are enabled to make any certain progress. Undoubtedly we shall have gained much merely in possessing some guide through this unknown region; and it is no less a saving of time and labour to be prevented from seeking or forcing an escape from our ignorance, where such is impossible. All this has already been achieved. There is, in this respect, no longer any impediment to our further progress. If, at the same time, we have returned again to the point from which we started, still the oppressive consciousness of an insurmountable obstacle has been removed, and we are in a position to press forward with renewed energy towards the desired object.

In this prospective and retrospective view of what has already been achieved, and what still remains to be done in this field, I will now attempt to present my readers with a delineation of plant life, as well individually as in its entire extent, constituting a portion of the vital phenomena of our planet.

The plant considered as a most skilfully-planned chemical laboratory ; a most ingenious mechanism for the play of physical forces ; as one of the simplest, and, consequently, most sublime structures ever designed or executed; the extent and distribution of this form of existence, made up of an indefinite number of parts; as well as the unity of style, and its developement in successive ages—these are the subjects which it is my intention to bring before you in the following letters.

Commencing with that which is most simple in plant life, the starting-point of our contemplations will be to trace back this complex structure to its several primary elements; whence we will follow out the construction of the individual objects ; the general plan to which, notwithstanding their diversity, they are all conformable, and, as we shall everywhere recognise, the same principle of unity ; finally, recombine the primary elements under a higher general conception.

‘May you possess inclination and patience to accompany me in the much-trodden, but unfortunately little-known, path [have marked out, and that not only without fatigue, but, perhaps, with a gain of intellectual activity.

Letter II. The Elementary Parts,of The Plant

None who have to any degree accustomed themselves to the contemplation of natural objects, will be disposed to regard the plant merely as an aggregate of leaves, stalks, flowers, etc., in which the figure, colour, nature of the substance, etc., have been determined and arranged by accident. A regular succession of the several organs, a certain normal developement and unity of form and colour, must have attracted the notice of all who have attentively examined even a few plants, and compared together their respective organs. It is, moreover, impossible to fail in arriving at a conviction that there is throughout the plant world a conformity to some general plan; a truth of which a very striking indication may, without difficulty, be recognized in the arrangement of the ultimate parts of which all plants are composed.

Before proceeding further in the consideration of this subject, I must request you to direct your attention for a while to these ultimate parts of plants, the stones, as it were, with which they build themselves up, which communicate to them solidity and durability, utility and beauty, and without which their existence would be altogether impossible. _ These ultimate parts of plants are not of such a nature as to belong to that class of material particles which are scarcely perceptible by the senses, still less are they analogous to atoms, but, on the contrary, always possess a definite bulk and a clearly distinguishable figure, which, although not in all instances perceptible by the naked eye, may by the aid of the microscope be studied even in their minutest details. It is, however, not only in the arrangement and connexion of these elementary parts, that our wonder is excited at the great art and skill which they display; this is still more evident in the structure of these parts

BOTANICAL LETTERS. Ff themselves. It is scarcely possible to conceive anything more wisely and artistically contrived than a cell. A delicate membranous vesicle imperceptible by the naked eye, covering a nucleus of partly liquid, partly solid substances in one case, and in another a hollow space, surrounded by a membrane almost stone-like in its hardness, the one being gradually produced from the other. The accompa- ee

nying figure is a considerablymagnified representation of a roundish somewhat flattened cell, with its contents partially visible through the delicate translucent membrane. How easy it is thus for the plant, by an appropriate distribution of these elements, so dissimilar in firmness, to employ the one here, the other there, according ag it may be requisite; and thus on the one hand the firmness and durability of the plant, on the other, its constant increase and growth, are rendered possible. The threads which are employed for making linen and other woven fabrics, the wood of trees, the hard shells of many fruits, consist of such old, indurated building-stones of the plant, while the younger and still soft cells, with their juicy and granular contents, frequently serve as the food of animals and of men.

The forms which these ultimate parts of plants present in the different organs of the plant, and in different plants, are not less remarkable. While one portion of them maintain their original globular figure, others become flattened, and resemble hewn stones of a square and other more or less regular figures, bounded by definite plane surfaces. Thus fig. 2 represents a cell perfectly flattened on all sides, the original spherical surface being only perceptible at the corners. It was therefore to some extent pardonable, that

Hig, 2.

these integral parts of plants should be mistaken for crystals, and that their formation should be regarded as analogous to that of the cubes of rock salt and fluor spar, or of the twelve faced figures of garnet.

Other forms, differing more widely from the vesicular form, occur in the long cylindrical or columnar cells, as shown in fig.3, and the flattened plate-like cells.

The substances which, like wood, | ; bark fibre, ete., are of such great utility for all the requirements of life, are nothing more nor less hci than such columnar plant-cells, a with pointed ends, by which ! they are, as it were, welded to each other, and form those tough elastic fibres. Fig. 4 is a magnified representation of several contiguous cylindrical cells, with ends pointed and joined together. Their thick walls render them firm and tough, and likewise communicate these characters to the bark which they constitute. It would carry us much too far to enter into a description of all those deviations from the primitive-cell form which, resembling sometimes familiar and sometimes irregular or variously-distorted figures, take a share in the composition of the plant organism. There is, however, one form which I cannot omit to mention, because it is one of the most elegant of minute forms, the so-called plant vessels.

While all cells, even when resembling pipes and lengthened cylinders, are closed at their ends, there are cylindrical cells which burst and form openings at their ends, where they join other similar cells. Tubes of greater or less length are thus formed, which, enclosed by other cells, constitute a system of mutually-communicating pipes, called vessels. A portion of

Fig. 3.

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E such a plant vessel, which, from the net-shaped markings upon its walls, is termed reticular vessel (vas reticulatum) is shown on a magnified scale in fig. 5. Generally speaking, a number of such vessels are grouped together, and surrounded by analogous, although upon the whole, different utricular cells, the whole constituting what has been termed vascular fibre.

The cells, according to their figure, form a kind of masonry, which is sometimes compact, sometimes porous in structure, consisting in different instances of rounded, quadratic, columnar or plate-shaped cells of various sizes, and which the anatomist technically calls cellular tissue. Thus fig. 6 represents cellular tissue, composed of roundish ellipsoidal and pear-shaped cells, which are merely in juxtaposition without being flattened, and consequently form a loose porous tissue (merenchyma). Fig. 6.

From the transparency of the cell membrane, the contents, consisting of green and other coloured vesicles, are distinctly perceptible; Fig. 7. Cellular tissue, composed of polygonal cells (parenchyma), the interior of which is exposed at the top and on one side by section. The individual cells are somewhat extended lengthways, and bounded by twelve planes. Their contents consist of a colourless watery fluid (cell sap) without any solid substances. The vascular fibres, from the circumstance that they usually possess greater firmness, may be compared to a skeleton ja OAS ey \ € Ss & a ana

WSS upon which the softer and more porous parts rest ; but im reality they do not in any other respect resemble these half-lifeless parts of the animal organism, at least during that period when they are still in full activity. When we consider that the

vascular fibres in their form, composition, developement, and — connexion, appear to exercise a determinative influence in all formations of cellular tissue, it may be possible to recognize in them the sketch in conformity with which the details of all plant structures are carried out. The mere observation of the _ network of ribs in a leaf might be sufficient to suggest this idea. Fig. 8 represents a portion of a palm stem, with three bundles of vessels, of which the two front ones are exposed by longitudinal, as well as transverse sections. In the larger of the two, at a, thin-walled wood cells are perceptible, at 6 a simple, and at c a reticulated spiral vessel, at d a bundle of so-called true vessels, at e thick-walled bast cells, which likewise recur in the smaller bundle of vessels. All these bundles of vessels are surrounded by parenchymatous cells ff.

« If what has already been adduced has served to afford some little insight into the structure of plants, I may be permitted to direct attention to a few other peculiarities which may be easily recognized in the arrangement of these elementary organs. From the term cellular tissue which has been applied to the masonry of the plant organism, it is very probable that those who have not had an opportunity of examining it by the aid of magnifying lenses, will form the erroneous opinion that it has in reality a greater resemblance to a tissue than to a piece of masonry. This, however, is not by any means the case. It is well known to every one that the peculiarity of a tissue consists in its being composed of a number of thread-like parts running in one direction, and united by similar ones running transversely. There is no kind of cementing substance, _ but the compactness and strength of the tissue are solely and alone determined by the interlacing of more or less uniform fibres.

No such arrangement is found in the so-called tissues of the plant. Its elementary parts are, without any exception, microscopic; they are simply situated beside and above each other; they are not interlaced, not even those which are tubular, except sometimes in mosses, alge, &c.; consequently the mass which they form resembles masonry rather than a tissue.

But this circumstance renders it imperatively necessary, in order that the whole may possess any degree of durability, that the individual elements should be united to each other. The cement or mortar by which this junction is effected is something very remarkable ; and we shall subsequently have occasion to consider it, for the present merely pointing out the necessity for it.

But it will be asked, are there not then in the plant organisths, consisting frequently of myriads of cells, arrangements which support the combination of individual parts as well as the firm connexion of larger masses? It would seem almost selfevident that such arrangements are absolutely necessary in all plants, in order that they may, even for a short period, withstand the influence of exterior mechanical violence.

And it certainly is so. The plant builds its secret chambers and roofs them over with such art—it employs in the construction of the stem which bears its entire weight, such groundsels, buttresses, and cramps—that an architect could not proceed more correctly. Must not the solid vascular fibres, thin above and thicker below, which, separately or arranged in circles, traverse the whole length of the stem, be regarded as actual buttresses against the storms and wind, with which the slender plant stem has to contend? Is it not by the most appropriate _ means that the longitudinal fibres of wood are clamped together by the so-called medullary rays? And when, besides this, we take into consideration the flexibility and elasticity of the elementary parts, it becomes intelligible, how, in spite of the elements, perpetually bent upon destruction, here the oak, there the feeble reed, wave their heads defiantly in the air.

I have spoken of the secret chambers in the interior of the plant, and possessing, in almost all instances, a particular form. These chambers, sometimes large, sometimes small, resembling regularly-shaped rooms, romantic caves, or even dilapidated ruins, are termed by the anatomist air-passages. They are shown on a_highly-maenified scale in fig. 9, as they appear in the leaf of Acorus calamus.

In this plant the air-passages aaaa are bounded by the most elegant cellular tissue. The regularly-shaped chambers which, as the above term indicates, contain nothing but air, are, for the most part, beautifully arched, elegantly constructed, and represent, in fact, microscopic grottoes, columned temples in the midst of the compact cellular tissue of the plant. Other larger cavities present, in their interior, the marks of decay but too distinctly. Much may be learnt in this respect from every blade of grass.

The most remarkable circumstance connected with these hollow spaces filled with air is, that they are, for the most part, connected with each other by means of much smaller passages which terminate outwards in innumerable open branches. The mouth of these minute shafts and galleries, leading into the interior by means of a great variety of channels, is always

Fig. 9.

delicately formed, and generally of such construction that it can be closed, and the communication between the atmosphere and the interior of the plant established or interrupted according to circumstances. Such mouth-like openings, which the botanist calls stomates or stomata, are so numerous, that upon a single square line of the leaf-surface of the common monkshood (Aconitum chamarum), nearly one thousand may be counted, and these do not occupy so much as one-tenth part of that space.

A piece of this leaf magnified two hundred times in diameter is represented in fig. 10; a is the exterior layer of cells at the upper side and consisting of plate-shaped cells; 0 is the exterior layer of cells on the under side, where the stomates are we SS

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“GS “ Uy = O fa) OAL/2 situated. At the sections it may be seen how these orifices, formed by two crescent-shaped cells, open into, with cavities, c, which communicate with each other throughout the entire cellular tissue of the leaf; d a layer of cylindrical cells near the upper surface; e a compound layer of irregular cells. It thus becomes intelligible how the atmospheric air penetrates even to the most remote parts of the plant organism, supplying it with various substances, and receiving others in exchange. Nevertheless, we should in vain seek for the air-channels and passages in those parts of the plant which are still in course of construction. It is not until after this has been completed that they are formed; they do not stand in any necessary relation to the new structures, and present the appearance rather of repositories, where things which are not capable of any further or immediate use are stored up.

In the plant such substances are represented by the resins, gum, ethereal oils, etc., which, although incapable of any application by the plant, are, nevertheless, of value to us. It thus frequently happens that we live upon the superfluities of nature, little suspecting that we are doing her a favour by taking something from her plenty.

As in all architectural works, requiring any great devas of accuracy, each stone must be Poy measured, especially formed and adapted for the position it is intended to occupy ; so is this equally necessary in the construction of the plant. There is no cell employed here whose form and dimensions have not been previously determined as with square and plumb-line, so that it is suited only to the place it occupies and for no other, fitting exactly into the depressions or elevations in its neighbouring cells. In observing a cellular tissue from any part of a plant, we cannot but be astonished at the beautifullyconstructed compact masonry in which the appropriate elements are not only arranged in order, but are likewise firmly united ' so as to form one mass. How beautifully, for instance, do the pointed ends of the columns and cylinders fit into the spaces left by the juxtaposition of similar elements, both above and below, thus forming ligneous and bark-fibres!—how close and tight are the brick-like cells which compose this masonry, which I ‘bests already compared to buttresses, the purpose of which is to protect the columnar wall against lateral pressure, and without which they would not possess that firmness which they everywhere present! Again, the whole of this is covered with a protecting mosaic pavement, extending over the entire surface of the plant. A portion of this epidermis, consisting of closely-fitting tabular cells is represented by fig. 11. The upper surface. of several of the cells is removed by section in order to expose the interior. It is impossible to imagine any roofing constructed with more closely-fitting tiles or a more delicate mosaic than the exterior cellular layer of plants, called, in technical language, the epidermis. Through this neither dust nor rain can penetrate, no particle of moisture can insinuate itself; and it is evident that the plant knows how to protect itself against atmospheric influences better than we can do in our most splendid and durable buildings.

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But, although by means of these adaptations the plant endeavours to maintain, as far as possible, its integrity ; it is not, on the other hand, entirely shut out from communion with the exterior world, from which, indeed, as we shall subsequently perceive, it derives all that is requisite for its existence. It is by means, partly of the air-cavities present on every part of the plant’s surface, that it receives whatever supplies it may require, and discharges its surplus products.

It is not difficult to believe that in a structure so delicate and well arranged, each part has a particular use and a definite purpose, so that an harmonious working of all the individual parts is rendered possible ; but that such a special utility extends even to the individual elements of the structure, cannot be inferred otherwise than from strict necessity. It is not until we know how each separate stone fulfils its functions in the perfect whole that we shall be in a position to form an opinion as to the stability, design, and harmony of the whole; and so long as there is no attempt made to obtain this knowledge, we may, indeed, vainly declaim upon the conformity to purpose and the beauty of the plant structure, but shall never be able, in accordance with the principles of science and art, to form a true and adequate conception of the structure of a leaf, or even a hair. or this reason it is that we cannot too highly esteem the endeavour, to establish the architecture of the plant upon a true scientific basis, and to obtain, in the knowledge of its elementary composition, a key to all that which is now a mystery to us. The man who has hitherto penetrated the furthest into this obscure region of research, who has attempted to examine stone for stone in their production and application, who has given us both ground-plans and elevations of some plant structures’ in which each element is marked with the number its architect intended for it, this man is Karl Nagel. It is undoubtedly from him that we may look for the unveiling, not only of the most simple, but likewise of the most complicated structures of the plant organism, which we have hitherto merely wondered at but not understood.

( Iv)

Letter III. Genesis Of The Cell

So far as we have yet proceeded, the comparison of the material composition of the plant with various parts of buildings has been of service in rendering our subject familiar and intelligible; but now the analogy begins to fail, inasmuch as we are about to inquire into the origin of the constructing material. Every architect procures his material from a greater or less distance; stone, bricks, lime, sand, water, and whatever else he may require, are brought to the place where the building is to be erected; and it is with these alone that he is able to carry out his work. But whence does the plant derive its stone, its mortar, etc., without which, in this as in the above case,the construction of any edifice of the same or similar elements would be impossible P