Rare Botany Literature From the Year 1892


The science of Botany includes everything relating to the Vegetable Kingdom, whether in a living or in a fossil state. Its object is not, as some have supposed, merely to name and arrange the vegetable productions of the globe. It embraces a consideration of the external forms of plants - of their anatomical structure, however minute - of the functions which they perform - of their arrangement and classification - of their distribution over the globe at the present and at former epochs - and of the uses to which they are subservient. It examines the plant in its earliest state of development, when it appears as a simple cell, and follows it through all its stages of progress until it attains maturity. It takes a comprehensive view of all the plants which cover the earth, from the minutest lichen or moss, only visible by the aid of the microscope, to the most gigantic productions of the tropics. It marks the relations which subsist between all members of the vegetable world, and traces the mode in which the most despised weeds contribute to the growth of the mighty denizens of the forest.

The plants which adorn the globe more or less in all countries must necessarily have attracted the attention of mankind from the earliest times. The science that treats of them dates back to the days of Solomen, for that wise monarch "spake of trees," from the cedar of Lebanon to the hyssop on the wall. The Chaldeans, Egyptians, and Greeks were the early cultivators of science, and Botany was not neglected, although the study of it was mixed up with crude speculations as to vegetable life, and as to the change of plants into animals. Aesculapius and his priests, the Asclepiades, who studied the art of medicine, had their attention directed to plants in a pharmaceutical point of view. About 300 years before Christ

Theophrastus wrote a History of plants, and described about 500 species used for the treatment of diseases. Dioscorides, a Greek writer, who appears to have flourished about the time of Nero, issued a work on Materia Medica. The elder Pliny described about a thousand plants, many of them famous for their medicinal virtues. Asiatic and Arabian writers also took up this subject. Little, however, was done in the science of Botany, properly so called, until the 16th century of the Christian era, when the revival of learning dispelled the darkness which had long hung over Europe. Brunfels, a physician of Bern, has been looked upon as the restorer of the science in Europe. He published a History of Plants, illustrated by figures, about the beginning of the 16th century.

One of the earliest attempts at a methodical arrangement of plants was made in Florence by Andrea's Caesalpinus, a native of Arezzo, some time professor of Botany at Padua, and afterwards physician to Pope Clement VIII.

He is called by Linnaeus primus verus systematicus. In his work De Plantis, published at lorence in 1583, he distributed the 1520 plants then known into fifteen classes - the distinguishing characteristics being from the fruits.

John Ray, a native of essex, did much to advance the science of botany. He was born in 1628, and died in 1705. He promulgated a system which may be considered as the dawn of the "natural system" of the present day (Ray, Methodus Plantarum, 1682). He separated flowering from flowerless plants, and divided the former into Dicotyledona and Monocotyledons. His orders were founded on a correct idea of the affinities of plants, and he far outstripped his contempories in his enlightened views of arrangement.

About the year 1670 Dr. Robert Morison of Aberdeen (Proeludia Botanica, 1672; Plantarium Historia Universalis, 1680) published a systematic arrangement of plants. He divided them into eighteen classes, distinguishing plants according as they were woody or herbaceous, and taking into account the nature of the flowers and fruit. In 1690 Rivinus ((Augustus Quirinus) paterno nomine Bachmann,

Introductio generalis in Rem Herbariam, Lipsiae, 1690). promulgated a classification founded chiefly on the forms of the flowers. Tournefort (Elemens de Botanique, 1694; Institutions Re Herbariae, 1700.) about the same time took up the subject of vegetable taxonomy. He was a contempory of Ray, and was professor of botany at Paris in 1683. He was long at the head of the French school of botany, and published a systematic arrangement in 1694-1700. He described about 8000 species of plants, and distributed them into twenty two classes, chiefly according to the form of the corolla, distinguishing herbs and under-shrubs on the one hand from the trees and shrubs on the other. The system of Tournefort was for a long time adopted on the continent, but was ultimately displaced by that of Linnaeus.

Carl von Linne, or, as he is commonly called, Linnaeus (System Naturae, 1735; Genera Plantarum, 1737; Philosophia Botanica, 1751; Species Plantarum, 1753) was born on the 23rd of May 1707, at the village of Rooahoolt (Rashult), in Smaland, a province of Sweden, where his father, Nicholas Linnaeus, was clergyman. He entered as a pupil at the University of Lund, and about the years 1727-28 was recieved into the house of Stobaeus, a physician in that city, where he had to struggle with great difficulties during his studies there. He aided Celsius in his Hierobotanicon. or account of the plants of the scripture, and he became assistant to Rudbeck, professor of botany. He afterwards travelled in Lapland, took his degree in Holland, visited England, and commenced practice in Stockholm, where he lectured on botany and mineralogy. He finally became professor of botany at Upsal, and was one of the most popular lecturers of the day. He died on the 8th of January 1778, in the 71st year of his age. His herbarium is now in the possession of the Linnean Society. One of his biographers, in summing up his merits, says, - "Educated in the severe school of adversity, accustomed from his earliest youth to put a high value on verbal accuracy and logical precision, endowed with a powerful understanding, and capable of undergoing immense fatigue, both of body and mind, Linnaeus produced a most important revolution in botanical science. He improved the distinctions of genera and species, introduced a better nomenclature on the binomial method, and invented a new and comprehensive system founded on the stamens and pistils. His verbal accuracy and the remarkable terseness of his technical language reduced the crude matter that was stored up in the folios of his predecessors into a form which was accessable to all men. He separated with singular skill the important from the unimportant in their descriptions. He arranged their endless synonyms with a patience and a lucid order that were quite inimitable. By requiring all species to be capable of a rigorous definition, not exceding twelve words, he purified botany from the endless varieties of the gardeners and herbalists; and by applying the same strict principles to genera, and reducing every character to its differential terms, he got rid of the cumberous descriptions of old writers. It is said of Linnaeus, that, although no man of science ever exercised a greater way, or had more enthusiastic admirers, yet his merit was not so much that of a discoverer as of a judicious and strenuous reformer. The knowledge which he displayed, and the value and simplicity of the improvements which he proposed, secured the universal adoption of his suggestions, and crowned him with a success altogether unparalled in the annals of the science."

The system of Linnaeus is founded on the sexes of plants, and hence it is often denominated the sexual system. It is called an artificial method, because it takes into account only a few marked characters in plants, and does not propose to unite them by natural affinities. It is an index to a department of the book of nature, and as such is useful to the student. It does not aspire to any higher charactor, and although it cannot be looked upon as a scientific and natural arrangement, still it has a certain facility of application which comends it to the tyro. In using it however, let it ever be remembered, that it will not of itself give the student any view of the true relations of plants as regards structure and properties, and that by leading to the discovery of the name of the plant, it is only a stepping stone to the natural system. Linnaeus himself claimed claimed nothing higher for it. He says - "Methodi Naturalis fragmenta studiose inquirenda sunt. Primum et ultimum hoc in botanicis desideratum est. Natura non facit saltus. Plantae omnes utrinque affinitatem monstrant, uti territorium in mappa geographica". Accordingly, besides his artificial index, he also promulgated fragments of a natural method of arrangement.

The Linnean system was strongly supported by Sir James Edward Smith, who adopted it in his English Flora, and who also became possessor of the Linnean collection. The system was for a long time the only one taught in the schools of Britain, even after it had been discarded by those in France and in many other Continental countries.

The foundation of Botanic Gardens during the 16th centuries did much in the way of advancing botany. They were at first appropriated chiefly to the cultivation of medicinal plants. This was especially the case at universities, where medical schools existed. The first Botanic Garden was established at Padua in 1545, and was followed by that of Pisa. The garden at Leyden dates from 1577, that at Leipsic from 1579. Gardens also early existed at Florence and Bologna. The Montpellier Garden was founded in 1592, that of Giessen in 1605, of Strasburg in 1620, of Altorf in 1625, and of Jena in 1629. The Jardin des Plantes at Paris was established in 1626, and the Upsal Garden in 1627. The Botanic Garden at Oxford was founded in 1632. The garden at Edinburgh was founded by Sir Andrew Balfour and Sir Robert Sibbald in 1670, and, under the name of the Physic Garden, was placed under the superintendence of James Sutherland, afterwards professor of botany in the university. The park and garden at Kew date from about 1730. The garden of the Royal Dublin Society at Glasnevin was opened about 1796; that of Trinity College, Dublin, in 1807; and that of Glasgow in 1818. The Madrid Garden dates from 1763, and that of Coimbra from 1773. Gesner states that at the end of the 18th century there were 1600 Botanic Gardens in Europe.

A new era dawned on botanical classification when Antoine Laurent de Jussieu appeared. He was born at Lyons in 1748, and was educated at Paris under the care of his uncle, Bernard de Jussieu. At an early age he became botanical demonstrator in the Jardin des Plantes, and was thus led to devote his time to the science of botany. Being called upon to arrange the plants in the garden, he necessarily had to consider the best method of doing so, and adopted a system founded in a certain degree on that of Ray, in which he embraced all the discoveries in organography, adopted the simplicity of the Linnean definitions, and displayed the natural affinities of plants. His Genera Plantarum, begun in 1778, and finally published in 1789, indicated an important advance in the principle of classification. Jussieu subsequently became professor of rural botany; he died in 1836 at the age of 88.

The system of Jussiea made its way slowly in Great Britain, and it was not until Robert Brown brought it under notice that it was adopted (Brown, Prodomus Florce NovaeHollandiae, 1810) It is now the basis of all natural classifications. One of the early Supporters of this natural method was Augustin Pyrame De Candolle, who was born in 1778, and who, after attending the lectures of Vaucher at Geneva, devoted himself to botanical pursuits. He subsequently prosecuted his studies at Paris, and lectured on botany at the College of France. He commenced his publications in 1802, and in 1804 he promulgated his Elementary Principles of Botany. In 1807 he became professor of botany at Montpellier, and in 1816 he was appointed to the chair of natural history at

Geneva, with the charge of the Botanic Garden. In that city he carried on his future botanical labours, and began his Prodromus Systematis Naturalis Regni Vegetabilis, which was intended to embrace an arrangement and description of all known plants. He was enabled to complete eight Volumes of the work before his death, and it has Since been carried on by his son Alphonse De Candolle, with the aid of other eminent botanists. It now embraces descriptions of the genera and species of Dicotyledonous plants. The system followed by De Candolle is a modification of that of Jussieu, and it is adopted more or less at the present day. De Candolle's own herbarium was extremely rich. He had visited and carefully examined many of the most extensive collections, especially those of Paris; and many entire collections, as well as separate families, on which he was Specially engaged, were from time to time submitted to his examination by their possessors He had thus opportunities of comparison greatly beyond what in ordinary circumstances fall to the lot of an individual.

His library, too, was stored with almost every important publication that could be required for his undertaking. With such ample materials, aided by his untiring zeal and the persevering energy of his character, he steadily pursued his allotted task, and only ceased to labour at it when he ceased to live. For some years his health declined, and it is to be feared that the severe and incessant attention which he paid to the elaboration of the great family of Compositae had made a deep inroad upon it. As a relaxation from his labours he undertook in the last years of his life a long journey, and attended the scientific meeting held at Turin; but he did not derive from this the anticipated improvement in his health, which gradually failed some until his death on the 9th September 1841. Since De Candolle's time various modifications of his system have been introduced by Endlicher, Lindley, Hooker, and Bentham.

In arranging plants according to a natural method, we require to have a thorough knowledge of structural and morphological botany, and hence we find that the advances made in these departments have materially aided the efforts of systematic botanists. Robert Brown, a Scottish botanist, was the first in this country to support and advocate,the natural system of classification. The publication of his Prodromus Florae Novae Hollandiae, according to the natural method, led the way to the adoption of that method in the universities and schools of Britain. Sir William (then Dr) Hooker, in his prelections in the University of Glasgow, and in his Numerous writings, ably supported Brown. John Lindley also came into the field, and in 1830 published the first edition of his Introduction to the Natural System. Dr Robert Kaye Greville and Dr Walker Arnott were able coadjutors, more especially in the department of Cryptogamic Botany. From the year 1832 up to 1859 great advances were made in systematic botany, both in Britain and on the continent of Europe. Endlicher's Enchiridion and Genera Plantarum, De Candolle's Prodromus, and Lindley's Vegetable Kingdom became the guides in systematic botany, according to the natural system.

The following remarks embrace the views of Mr Bentham on the change from the Linnean to the natural system of classification:—" The change from the technical to the scientific study of plants was now complete. The Linnean platform, established on the relation of genera and species, had now been so long and so universally adopted as the basis or starting point, that the credit due to its founder was almost forgotten, and it was superseded by the Jussiean method, although it was chiefly by the consistent following out the principles laid down by Linnaeus himself that the change had been effected. Plants were now grouped upon a philosophical study of their affinities, whether morphological, structural, or physiological." In all classification it is necessary to define what is meant by species. The usual definition of the term has been that a species (as regards the present epoeh of the earth's history) is an assemblage of individuals having characters in common, and coming from an original stock or protoplast, and their Seeds producing similar individuals. It was also supposed that variation in species was restrained within certain limits, and that varieties had a tendency to revert to the parent form. The view, however, adopted by many now-a-days is, that the tendency to variation is eontinuous, and that, after a lapse of long periods of time, and under the influence of varying external conditions, the descendants from a common stock may exhibit the differences which characterize distinct species. These are the views which are advanced by Darwin, and which imply a complete revolution m our idea of species. This theory is thus stated by Bentham:

1. That although the whole of the numerous offspnng of an individual plant resemble their parent in all main points there are slight individual differences.

2. That among the few who survive for further propagation, the great majority, under ordinary circumstances, are those which most resemble their parent, ard thus the Species is continued without material variation.

3. That there are, however, occasions when certain individuals, with slightly diverging characters, may survive and reproduce races, in which these divergencies are continued even with increased intensity, thus producing Varieties.

4. That in the course of an indefinite number of generations circumstances may induce such an inerease in this divergency, that some of these new races will no longer readily propagate with each other, and the varieties become New Species, more and more marked as the unaltered or less altered races, descendants of the common parent, have become extinct.

5. That these species have in their turn become the parents or groups of speeies, that is Genera, Orders, &c., of a higher and higher grade, according to the remoteness of the common parent, and more or less marked, according to the extinction or preservation of unaltered primary, or less altered intermediate, forms.

As there is thus no difference but in degree between a variety and a species, between a species and a genus, between a genus and order, all disputes as to the precise grade to which a group really belongs are vain. It is left in a great measure to the judgment of the systernatist, with reference as much to the use to be made of his method as to the actual state of things, how far he should go in dividing and subdividing, and to which of the grades of division and subdivision he shall give the names of Orders, Sub-orders, Tribes, Genera, Subgenera, Sections, Species, Subspecies Varieties &c., with the consequent nomenclature.

Such a systematic arrangement is founded on a hypothesis which, so far as the present flora of the globe is conerned, cannot be demonstrated. Conjecture is hazarded as to the present epoch of the earth's history, by extending back to unlimited ages. If the theory is consistent with what. we see around us, and is founded on plausible grounds, then we mast think that we have ascertained the plan followed by the great Creator, Designer, and Upholder of all things, that we have been able to ascertain and follow His workings, and the mode in which He has created the diverse plants which have covered our globe in tune and space. This new phase of systematic botany, however, requires more definite data to lead to its adoption as an explanation of the plan of creation.

The Physiology of plants did not keep pace with the advance in Classification. Grew and Malpighi were the earliest discoverers in this department of botany. Hales also contributed to it by his observations on the motion of fluids in plants. The subject of fertilization was one which early excited attention. The idea of the existence of separate sexes in Pants was entertained in early times, long before separate male and female organs had been demonstrated. The production of Dates in Egypt, by bringing two kinds of flowers into contact, proves that in very remote periods some notions were entertaned on the subJect. Female Date Palms only were cultivated, and wild ones were brought from the desert in order to fertilize them. Herodotus informs us that the Babylonians knew of old that there were male and female Date-trees, and that the female required the concurrence of the male to became fertile. This fact was also known to the Egyptians, the Phoenicians, and other nations of Asla and Africa. The Babylonians suspended male clusters from wild Dates over the females; but they seem to have supposed that the fertility thas produced depended on the Presence of small flies among the wild flowers, which, by entering the female flowers, caused them to set and ripen. Theophrastus, who succeeded Aristotle in his school in the 114th Olympiad, frequently mentions the sexes of plants, but he does not appear to have determined the organs of reproduction. Pliny, who flourished under Vespasian, speaks particularly of a male and female palm, but his statements are not founded on any real knowledge of the organs. From Theophrastus down to Caesalpinus, who died at Rome in 1603, there does not appear to have been any attention paid to the reproductive organs of plants. Caesalpinus had his attention directed to the subject, and he speaks of a halitus or emenation from the male plants causing fertility in the female.

Grew seems to have been the first to describe, in a paper on the Anatomy of plants, read before the Royal Society in November 1676, the functions of the stamens and pistils. Up to this period all was vague conjecture. Grew speaks of the attire, or the stamens, as being the male parts, and refers to conversations with Sir Thomas Millington, Savilian professor at Oxford, to whom the credit of the sexual theory seems really to belong. Grew says that, "when the attire or apices break or open, the globules or dust falls down on the seedcase or uterus, and touches it with a profilic virtue." Ray adopted Grew's views, and states various arguments to prove their correctness in the preface to his work on European plants, published in 1694. In 1694 Camerarius, professor od Botany and medicine at Tubingen, published a letter on the sexes of plants, in which he refers to the stamens and pistils as the organs of reproduction, and states the difficulties he had encountered in determining the organs of Cryptogamic plants. In 1703 Samuel Morland, in a paper read before the Royal Society, stated that the farina (pollen) is a congeries of seminal plants, one of which must be conveyed into every ovum or seed before it can become prolific. In this remarkable statement he seems to anticipate in part the discoveries afterwards made as to pollen tubes, and more particularly the peculiar views promulgated by Schleiden. In 1711 Geoffroy, in a memoir presented to the Royal Academy at Paris, supported the views of Grew and others as to the sexes of plants. He states that the germ is never to be seen in the seed till the apices (anthers) shed their dust; and that if the stamina be cut out before the apices open, the seed will either not ripen, or be barren if it ripens. He mentions two experiments made by him to prove this - one by cutting off the staminal flowers in Maize, and the other by rearing the female plant of Mercurialis apart from the male. In these instances most of the flowers were abortive, but a few were fertile, which he attributes to the dust of the apices having been wafted by the wind from other plants.

Linnaeus was the next botanical author who took up the subject, and by his sexual system he may be said to have opened a new era in the history of botany. He first published his views in 1736, and he thus writes - "Antheras et stigmata constituere sexum plantarum, a palmicolis, Millingtono, Grewio, Rayo, Camerario, Godofredo, Morlando, Villantio, Blairio, Jussievio, Bradleyo, Royeno, Logano, &c., dedectum, descriptum, et pro infallibili assumptum; nec ullum, apertis oculis considerantem cujuscunque plantae flores, latere potest." He divided plants into sexual and asexual, the former being Phanerogamous or flowering, and the latter Cryptogamous or flowerless. In the latter division of plants he could not detect stamens and pistuls, and he did not investigate the mode in which their germs were produced. He was no physiologist, and did not promulgate any views as to the embryogenic process. His followers were chiefly engaged in the arrangement and classification of plants, and while descriptive botany made great advances the physiological department of the science was neglected. His views were not, however, adopted at once by all, for we find Alston stating arguments against them in his Dissertation on the Sexes of Plants. Alston's observations were founded on what occured in certain unisexual plants, such as Mercurialis, Spinach, Hemp, Hop, and Byrony. The conclusions at which he arrives are those of Pontedera, that the pollen is not in all flowering plants necessary for impregnation, for that fertile seeds can be produced without its influence.

He supports parthenogenesis in some plants. Soon after the promulgation of Linnaeus's method of classification, the attention of botanists was directed to the study of Cryptogamic plants, and the valuable work of Hedwig on the reproductive organs of Mosses made its appearance in 1782. He was one of the first to point out the existance of certain cellular bodies in these plants which appeared to perform the functions of reproductive organs, and to them the name of antheridia and pistillidia were given. This opened up a new field of research, and led the way in the study of Cryptogamic reproduction, which has since been much advanced by the labours of numerous botanical inquirers. The interesting observations of Morland, already quoted, seem to have been neglected, and no one attempted to follow in the path which he had pointed out. Botanists were for a long time content to know that the scattering of the pollen from the anther, and its application to the stigma, were necessary for the production of perfect seed, but the stages of the processof fertilization remained unexplored. The matter seemed involved in mystery, and no one attempted to raise the viel which hung over the subject of embryogeny. The general view was, that the embryo originated in the ovule, which was in some obscure manner fertilized by the pollen.

In 1815 Treviranus roused the attention of botanists to the development of the embryo, but although he made valuable researches, he did not add much in the way of new information. In 1823 Amici discovered the existance of pollen tubes, and he was followed by Brongniart and Brown. The latter traced the tubes as far as the nucleus of the ovule. These important discoveries mark a new epoch in embryology, and may be said to be the foundation of the views now entertained by physiologists, which have been materially aided by the subsequent elucidation of the process of cytogenesis, or cell-development, by Schleiden, Schwann, Mohl, and others. The whole subject has been investigated recently with great assiduity and zeal by physiologists, as regards both Cryptogamous and Phanerogamous plants. The formation of germinal vesicles in the ovule, and the development of the embryo in flowering plants, have been fully considered by Griffith, Schleiden, Mirbel, Spach, Meyen, Schacht, Mohl, Unger, Naudin, Radlkofer, and others; the embryogenic process in Coniferous plants and in the higher Cryptogams by Hofmeister, Henfrey, Suminski, Mettenius, Strasburger, Eichler, Baillon, Cohn, Pringsheim, Millardet; and that of the lower Cryptogams by Thuret, Bornet, Decaisne, and Tulasne. The observations of Darwin as to the fertilization of Orchids, Primula, Linum, and Lythrum, and the part which insects take in this function, have opened up a new erain Physiological Botany. He has been followed by Hermann Muller. Darwin's experiments in reference to the movements of climbing and twining plants, and of leaves in insectivorous plants, have opened up a wide field of inquiry which he has cultivated with eminent sucess and with most important results. Among other authors who have contributed to the advance of Vegetable Physiology may be named Hoffmann, Sachs, Van Tieghem, Prillieux, Deherain, and Famintzen. We have thus been enabled to come to certain general conclusions on this obsecure subject, and future observers have been directed in the proper path of investigation.

In the Physiological department of botany the most important researches have been made by French and German botanists. The laboratories in connection with schools in Germany offer facilities for study which do not exist to the same extent in Britain. Physiological researches demand not only a Botanic Garden with its appendages, but apparatus of various kinds, means of prosecuting histological and chemical investigations, physical experiments, and observations by the spectroscope. Our schools require them not only lecture-rooms, but labratories well fitted up with all the needful appliances, and salaried assistants to aid the teachers i their demonstrations and the pupils in their practical work.

The department of Geographical Botany has made rapid advance by means of the various scientific expeditions which have been sent to all quarters of the globe; and the question of the mode in which the floras of islands and of continents have been formed has given rise to important speculations by such emminent botanical travellers as Darwin and Hooker. The latter has published a valuable paper on insular floras. Under this department the connection between climate and vegetation has been carefully studied both by botanists and by meteorologists. Among the contributers to this department of botany the following authors may be noticed - Humboldt, Schouw, Meyen, Berghaus, Martius, Harvey, Hooker.

The subject of Palaeontological Botany has been much advanced of late by the researches of botanists and geologists. The use of the microscope in the examination of tissues has aided much in the determination of fossil plants. The more accurate study of Oceanography has also been the means of correcting errors in diagnosis. The nature of the climate at different epochs of the earths history has also been determined from the character of the flora. The works of Brongniart, Goeppert, and Schimper have advanced this department of science. Among others who have contributed valuable papers on the subject mat be noticed Heer, who has made observations on the Miocene flora, especially in Artic regions; Saporta, who has examined the Tertiary flora; Dawson and Lequereux, who have reported on the Canadian and American fossil plants; and Williamson, who has made a careful examination of many of the coal fossils, and whose excellent drawings of structure have opened a new light on the character of many of the genera. Delineations of fossils by Witham, Lindley and Hutton, and Carruthers, have tended much to advance our knowledge of the fossil flora of Britain. Botany may be divided into the following departments; -

1. Structural Botany, having reference to the anatomical structure of the various parts of plants, including Vegetable Histology, or the microscopic examination of tissues.

2. Morphological Botany, the study of the form of plants and their organs - (these two departments are often included under the general term of Organography).

3. Physiological Botany, by some termed Organology, the study of the life of the entire plant and its organs, or the consideration of the functions of the living plant.

4. Systematic Botany, The arrangement and classification of plants.

5. Geographical Botany, the consideration of the mode in which plants are distributed over the different regions of the globe.

6. Palaeontological Botany, the study of the forms and structures of the plants found in a fossil state in the various strata of which the earth is composed.