Popular Science Monthly/Volume 22/December 1882/Sketch of Matthias Jacob Schleiden

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"TWO names," says M. Leo Herrera, in the "Revue Scientifique," "are inseparably connected with that grand movement of the biological sciences that began about 1838, and of which we to-day contemplate the superb bloom—Schleiden and Schwann. The two laid the foundations of the cellular theory. Both exercised a powerful influence over their contemporaries; both rendered lasting services to science through their teaching, their pupils, their ideas, and even through their errors."

Schleiden devoted himself variously to law, medicine, the natural sciences, and philosophy, and his works bear the marks of those diversified studies: but he was, above all, a botanist; it was under this title that he became famous, and by this his name must endure.

Matthias Jacob Schleiden was the son of the physicist, Andreas Benedict Schleiden, and was born in Hamburg, April 5, 1804. On quitting the gymnasium he entered upon the study of the law at Heidelberg in 1824. He received his degree in 1827, and had entered upon the practice of his profession in his native city, when, in 1831, he concluded that the natural sciences were more to his taste than the law. With the encouragement of his father, he returned to the university, and studied medicine at Göttingen—where he enjoyed the instructions of Bartling in botany—and the natural sciences at Berlin, where his uncle, the botanist Horkel, enlisted his special interest in that branch. In 1839 he was appointed, on the recommendation of Humboldt it is said, Adjunct Professor of Botany at Jena, where he continued to teach in the chair of that science till 1862.

Schleiden was thirty-three years old when he published his first works; the scientific collections from 1837 to 1852 contain twenty-seven memoirs contributed by him. The most striking of these essays and the ones which contributed most directly to his rapid rise to eminence, were those in which he propounded his theories of the origin of plant-cells and of fructification. These were the "Beitrage zu Phytogenesis" "Contributions to Phytogenesis," 1838), and "Ueber Bildung des Eichens und Entstehung des Embryos beim Phanerogamen" ("On Formation of the Ovule and Origin of the Embryo in Phanerogams," 1839)—his "most remarkable, most revolutionary, and most erroneous works," which astonished the world, "just as he had barely made himself known by a few anatomical and organo-genical researches." Both of these works called forth lively responses. They were translated into English and French. They were commented upon and discussed, and were the subject of passionate debates; in short, inquiry was awakened, and an impulse was given to investigation, the force of which has not slackened to this day.

The theory of cells, as given in the "Phytogenesis," may be briefly stated as follows: There are two points in a plant well adapted for a ready and safe observation of the production of a new organization; these are the embryo-sac and end of the pollen-tube (according to his fertilization theory, the first cells of the embryo should form there, while in reality this is not the case). At both points, the formation of nuclei causes turbidity in the homogeneous gum-solution these increase in size, and soon cytoblasts (a granular coagulation) appear. In the free state the cytoblasts increase rapidly until they attain a certain size, when they are surmounted by a fine diaphanous bubble; this is the young cell, at first a segment of a sphere, its plane side formed by cytoblasts, and its convex side by young cells (the cell-epidermis) similar to a watch-crystal on a watch. Gradually the bubble expands, becomes more consistent, and the wall is composed of cytoblasts and of a gelatinous substance. The cell grows, overlaps the cytoblasts, and then increases so rapidly that the cytoblast appears as a small nucleus inclosed in a duplicature of the cell-wall. As the growth progresses, the mutual pressure, exerted by the cells upon one another, causes a certain regularity of form, frequently that of the rhombendodecahedron. Only after the resorption of the cytoblasts the formation of secondary deposits begins on the inner surface of the cell-wall. Scbleiden assumes the process thus described to be the general law of formation for the vegetable cell-tissues in the phanerogams. This theory was conceived while Schwann was still engaged with his theory of the origin and propagation of animal cells. Schwann has, in fact, acknowledged in his "Microscopic Researches" that Scbleiden communicated his observations on the subject to him before publishing them, and thus gave him the light that showed him the way to his own results. So it has come to pass that, by means of the joint labors of these two men, the cell has been recognized as the peculiar element in both kingdoms of organic nature, and all the processes of vegetable and animal life have been located in its little laboratory.

Schleiden's theory has been proved to be a premature generalization, based upon incomplete and inaccurate observations, and has been refuted by Nägeli; but, incorrect and of little consequence as it was in itself, it has also proved to be the grain of ferment which has worked a transformation and revivification of biological science.

Schleiden's theory of fructification was announced just at the time (1839) when those who denied sexuality in plants had seemed to carry the day, and all botanists had agreed, to use the language of M. Herrera, in attributing the production of the embryo to the ovule, while allowing to the pollen only a simple action of fertilization. "All at once a botanist, already celebrated, proclaimed that he had seen the embryo forming in the grain of pollen and penetrating the ovule with the pollenical tube. This unexpected animalculist was Schleiden. His animalculism was, however, limited to the vegetable kingdom. He did not aspire to extend it to the other kingdom. To explain the contradiction which thus appeared between the fecundation of animals and that of plants, he regarded the vegetable ovule as a male organ, and the grain of pollen, producer of the embryo, as a female organ. The announcement of this discovery came like a clap of thunder. It soon had enthusiastic partisans and angry critics. The critics were in the right, the partisans were at fault; but what does it matter now? Schleiden had again given a powerful impulse to the spirit of investigation, and that is the essential thing. His memoir, otherwise, is far from containing anything good or exact."

"Schleiden had disciples who were eager to adopt the doctrine of their master and promulgate it. At the same time, however, Mirbel and Brongniart skillfully guarded their opinions, and Meyen attempted a formal refutation of the new theory. A general and hot contest arose and lasted for more than twenty years, in which all the distinguished botanists of every country became engaged. Amici in 1842 confirmed and extended the previous observations of Mirbel, Spach, and Brongniart. He asserted that he had seen the embryo produced at the expense of a part of the embryonary sac, and this seemed to settle the question against Schleiden. Schleiden, however, hastened quickly to refute Amici's assertion. The great Modenese naturalist returned to the charge with his observations on the orchids. In 1850 the Academy of Amsterdam crowned a work of Schacht, a disciple of Schleiden's, who vigorously defended his master's theory. Tulasne, Hugo Mohl, Brongniart, Ch. Midler, and Hofmeister came forward to oppose it. It gave way and seemed to be dead; then it rose again and renewed the contest. On the 19th of December, 1854, Schacht triumphantly announced to the congress of naturalists, at Berlin, that a young man, Th. Deecke, a partisan, like himself, of Schleiden's doctrine, but more fortunate than he, had succeeded in making a microscopic preparation of Pedicularis sylvatica which was of such a nature as to reduce for ever to silence the adversaries of that theory. This preparation had a great repute. The story was passed around from city to city, but, while Schacht pretended that it was unanswerable, Hugo Mohl declared that he saw nothing conclusive in it. This was the last flickering of the theory of Schleiden. Radekofer published numerous observations against it in 1856, and announced at the same time that Schleiden had himself abandoned the theory which he had put forward. Shortly afterward, Schacht also acknowledged that he had been in error, and the theory, left dead on the battle-field, was buried for good."

With the vitality which Schleiden and his contemporaries had infused into botany a new era was inaugurated for the science. To mark its coming and extend the comprehension of the principles and aspirations. of the new school, were needed a compendious and methodical treatise for students and a popular book for readers. Schleiden composed both. The time had passed when the study of living beings should form a separate branch of science, and when those who discarded the dry enumerations of the classifiers would have to fall into the ideal reveries of the "philosophers of nature." It needed to be shown that botany was not the mere dry skeleton which the former would make of it, and that it did not require the tinsel with which the latter assumed to adorn it. In the "Grundzüge der wissenschaftlichen Botanik" ("Elements of Scientific Botany") of Schleiden, the science was for the first time treated entirely according to the inductive method, as physics and chemistry had already been considered; and the different branches of science, till very recently still isolated and almost hostile, were made to interpenetrate and mutually illustrate each other. The book was well adapted to enlarge the scientific horizon, and to inspire youth and develop the spirit of research in them. The reading of the first few pages of the book is sufficient to give this impression of its motive. The dedication to Alexander von Humboldt, unquestionably the man of most universal knowledge of his time, attests the author's desire to connect botany intimately with the other sciences. The capital importance which he rightly attached to method is affirmed by the title which he gave to the second edition of his treatise—"Botany as an Inductive Science." The very first lines of his preface show that he does not intend to deal with a science of words and dreams, but of observation, experiment, and independent thought. "Whoever thinks he can learn botany in this book may as well put it aside at once without reading it, for botany can not be learned from books." In this work, says Dr. Karl Midler, Schleiden expressed for the first time a full comprehension that natural science was essentially a history of development, and expressed it in such a manner as to attract enthusiastic youth to his doctrine while he incurred the hostility of the elders in science. Among the salient features of his theory are the ascription of a leading part in all morphological questions to the study of the development of the organs, and his putting of the cryptogams upon a footing of equality in consideration with phanerogams. Perhaps no innovation in science has been so fruitful as the step which gave the prominent place in study to the first, stages rather than to adult forms, to inferior beings rather than to elevated and complex groups.

One passage in the "Grundzüge" is worthy of especial remark, for the evidence it bears of the completeness of the author's rejection of the sterile categories of the older philosophers, and of his having been endowed with the scientific spirit of later times. "The division of natural objects into organic and inorganic could only have originated at a time when students had only the two extremes to consider. A person comparing a lion with a piece of chalk would, doubtless, say that the difference is evident to all the senses. But let him compare the small, almost spherical crystals of oxide of iron with the minute, spherical articulations of Ehrenberg's Gallionella ferruginea, which likewise consist almost exclusively of oxide of iron, and undeniably represent organic forms, either animal or vegetable: the crude antithesis disappears at once, and all who reflect will conceive for science the possibility, still distant, of bringing the formation of both kinds under the same law of nature. There are in nature thousands of these apparent leaps, like that from the inorganic to the organism, in regard to which attentive observation will reveal to us gradual differences instead of a specific distinction."

This work excited a wide-spread and virulent opposition in consequence of the bitterness of its polemics, its severe criticisms of the didactic methods of investigation and the dry systems in vogue at the time, and its sharp personalities. The book was called libelous in France, for the author, according to Dr. Karl Midler, seemed to speak well of no one except Robert Brown and Hugh Mohl, "the two living men whom he most admired," and was not sparing in his criticisms of them. "With incomparable acuteness, and with equal acerbity against living and dead, he poured out such a flood of botanical satires and personal antipathies that he would have had to be a god to escape the reaction against his attacks; and the day when this was to take place was not long in coming." Yet, he did not let his vehement criticisms go forth without making an excuse for them. It was that "enough merit still exists among true naturalists to permit us to leave the business of mutual admiration to the literary beggars of belles-lettres journalism." Notwithstanding this opposition, the current in favor of Schleiden's conception of the object of scientific study could not be diverted; and the medical faculty of Tubingen, one of whose members was Schleiden's most eminent opponent in a number of special cases, replied to his acrid charges by conferring upon him its honorary degree.

Schleiden's other book, "Die Pflanze und ihr Leben" ("The Plant and its Life"), the object of which was to popularize botany, had a brilliant success. The first edition of 1848 was rapidly followed by other editions, and the work appeared in the course of the next ten years in one French, one Dutch, and two English translations. The author, in the preface to this work, defines his object as follows: "Most people of the world, even the most enlightened, are still in the habit of regarding the botanist as a dealer in barbarous Latin names, as a man who gathers flowers, names them, dries them, and wraps them in paper, and all of whose wisdom consists in determining and classifying this hay which he has collected with such great pains. This portrait of the botanist was, alas! recently true; but, now that it is no longer applicable to the majority among us, I have been grieved to see that many still hold to it. So I have endeavored in these lectures to place within the reach of all the real principles of botanical science, and to show how it is intimately connected with all the leading problems of philosophy and the natural sciences." Beginning with an account of the structure of plants as revealed by the eye and the microscope, he recognizes the labors of Mohl, Nägeli, Payen, and others, and even has the courage to admit that they have damaged his own theory of the genesis of cells. The discussion of the nutritive elements of plants gives him occasion to do justice to Hales, De Saussure, Boussingault, and Liebig, his long-time adversary. Then, from applied botany, he passes to the two sciences which were quite new at the time, of botanical geography and paleontology; and he concludes with a chapter in which the whole subject receives an æsthetical treatment.

Before this work appeared, however, Schleiden, discouraged by the success of the assaults upon his pet theories, had suffered a loss of confidence in himself and of relish for pure botany. His last work in pure science was a note on the fructification of the Rhizocarps, published in 1846; the "Zeitschrift fur wissenschaftliche Botanik" ("Journal of Scientific Botany"), which he, with Nägeli, had founded in 1844, ceased to appear at the same time.

After completing the third edition of the "Grundzüge" in 1850, the failure to modify or improve which in any essential particular emphasizes his loss of relish for the pursuit, Schleiden withdrew almost entirely from the arena of scientific botany. He turned his attention to anthropology; and, finally, in 1862, resigned his chair of botany at Jena, whence he repaired to Dresden. "Still, however, the old halo wavered around his head," and he was called to the University of Dorpat, as Professor of Botany and Anthropology, with the rank of a Russian councilor of state. He was not permitted to stay long there, however; for, being accustomed to express himself too freely on ecclesiastical subjects in his public addresses, he soon raised a strong party against himself, and was obliged to resign his second professorship in 1864. From this time till the end of his life he resided by turns at Dresden, Frankfort-on-the-Main, Wiesbaden, and again at Frankfort, where he died on the 23d of June, 1881. Death surprised him while he was engaged upon a work on the horse, one of three monographs in which he designed to illustrate the influence of natural agents upon civilization, choosing as examples from each of the three kingdoms—salt, the rose, and the horse. The two of these treatises which we possess are models of their kind.

The character of Schleiden may be read in his writings. Ardent and enthusiastic, he never praised or blamed by halves; but, in his most animated polemics, there appears a sincere and disinterested conviction that commands respect. To the end of his life he retained a degree of youthfulness in his thought and style. He had the imagination of a poet, with the scientific spirit to guide it; and instead of being carried away, or letting his readers be carried away, in his flights, he is constantly calling them back to reality and reason. He erred in that he relied too much on his own deductions, and did not sufficiently appreciate the importance of verifying them by experiment and close observation. Thus it came about, as Karl Midler has remarked, that he has given us, in his works, "a diversified mixture of philosophical prepossession, jejune observation, and fanciful description. Nevertheless, despite his peculiar weaknesses, his followers recognize him as a reformer of botany, and allot him a permanent and eminent place in the history of that science."

Schleiden's works are numerous; we will mention "Grundzüge der wissenschaftlichen Botanik" (two vols., Leipsic, 1842-'43) ("Elements of Scientific Botany"), fourth edition 1861, translated into English by Dr. Lankester, London, 1849; "Die Pflanz und ihr Leben" ("The Plant and its Life"), sixth edition, Leipsic, 1864, translated by Professor Henfrey, London, 1848; "Handbuch der medicinisch pharmaceutischen Botanik" ("Manual of Medicinal Pharmaceutical Botany"), (Leipsic, 1852); "Studien" ("Studies"), (second edition 1857); "Handbuch der botanischen Pharmakognosie" ("Manual of Botanical Pharmacology"), (Leipsic, 1857); "Die Landenge von Suez" ("The Isthmus of Suez"), (1858); "Zur Theorie des Erkennens durch den Gesichtssinn" ("Additions to the Theory of Determination by the Sense of Sight"), (Leipsic, 1861); "Geognostische Beschreibung des Saalthals bei Jena" ("Geognostic Description of the Valley of the Saal at Jena"), (Leipsic, 1846); "Beiträge zur Botanik" ("Additions to Botany); "Pflanzen und Thierphysiologie in Encyklopädie der theoretischen Naturwissenschaft" ("Physiology of Plants and Animals in Encyclopædia for Theoretical Natural Philosophy"), (Braunschweig, 1850); "Gedichte" (pseudonym "Ernst"), ("Poems") (nom deplume "Ernst"), 1858; "Das Meer" ("The Ocean"), (Berlin, 1865); "Baum und Wald" ("Tree and Forest"), (1870); "Uber den Materialismus der neueren deutschen Naturwissenschaft" ("Materialism in Modern German Natural Philosophy"); "Die Bedeutung der Juden für die Erhaltung und Wiederbelebung der "Wissenschaften im Mittelalter" ("The Signification of the Jews in the Conservation and Revival of the Sciences in the Middle Ages")—a work demonstrating the high degree of culture maintained by the Jews, even during the darkest periods of history, and the important part they had in the development of science and letters in Christendom—(1877); "Die Romantik des Martyriums bei den Juden im Mittelalter" ("The Romance of the Jewish Martyrology of the Middle Ages"), (Leipsic, 1878).