Morphology, Plant

Morphology, Plant

 

(also phytomorphology), the study of the structure and form development of plants in their individual and evolutionary-historical development. It is one of the most important branches of botany. As plant morphology developed, the following independent sciences were established: plant anatomy, which studies the tissue and cell structure of organs; plant embryology, which studies embryo development; and cytology, which studies cell structure and development. Thus, plant morphology, in the narrow sense, primarily studies the form development and structure of an organism; however, it also is concerned with regularities on the population-species level, inasmuch as it deals with the evolution of form.

Principal problems and methods The principal concerns of plant morphology are identifying the morphological diversity of plants in nature, studying the regularities of the structure and interrelated distribution of organs and their systems, analyzing the changes in a plant’s total structure and in its individual organs in the course of its independent development (ontomorphogenesis), revealing the origins of plant organs during the evolution of the plant world (plant morphogenesis), and investigating the effects of various external and internal factors on form development. Thus, plant morphology does not limit itself to the description of certain types of structure but also strives to explain the dynamics of structures and their origins. The principles of biological organization, that is, the internal interrelationships of all processes and structures in an organism, are manifested in the organism’s external form.

Theoretical plant morphology distinguishes between two interrelated and complementary approaches to the interpretation of morphological data. One approach reveals the reasons for the origin of any given form (from the point of view of the factors immediately acting on morphogenesis). The other explains the biological significance of certain forms for the life activity of the organisms (from the point of view of adaptability), which leads to the preservation of certain forms in the process of natural selection.

Morphological research is conducted by three principal methods: descriptive, comparative, and experimental. The first consists of descriptions of the forms of organs and their systems (organography). Comparative morphological methods are used to classify descriptive material. They are also used to study the changes an organism and its organs undergo as a result of aging (comparative-ontogenetic method), to explain the evolution of organs by comparing them with plants of different taxonomic groups (comparative-phylogenetic method), and to study the influence of the external environment (comparative-ecological method). Experimental morphological research involves the creation of controlled external conditions; the morphological reactions of plants to these artificial conditions are studied. The internal interrelationships between the organs of a living plant are examined by means of surgical intervention.

Plant morphology is closely related to other branches of botany, such as paleobotany, plant taxonomy and phylogeny (plant forms are the result of a long historical development and reflect the plants’ similarities), plant physiology (the dependence of form on function), ecology, phytogeography and geobotany (dependence of form on external environment), genetics (inheritance and acquisition of new morphological characters), and horticulture.

Brief historical survey The beginnings of plant morphology, and of botany in general, go back to early antiquity. The terminology of morphological description of plants was introduced principally in the 17th century, at which time the first theoretical generalizations were made by the Italian scientists A. Cesalpino and M. Malpighi and the German scientist J. Jung. However, the establishment of plant morphology as an independent science took place in the late 18th century with the publication in 1790 of J. W. von Goethe’s Essay on the Metamorphosis of Plants. Goethe introduced the term “morphology” in 1817. He emphasized the similarities in the diversity of forms in plant organs and showed that all the organs of a shoot, from the cotyledon to the flower parts represent modifications (metamorphoses) of the same elementary lateral organ—the leaf (type-leaf). The cause of metamorphoses, according to Goethe, is a change in the nutrient intake of newly formed leaves to the extent that the shoot apex moves away from the soil.

Goethe’s works greatly influenced the subsequent development of plant morphology. However, in the “type” concept of organs, which was for Goethe absolutely real, lay the possibility of an idealist approach, that is, the interpretation of the “type” as the “idea” of an organ embodied in different forms. Indeed, many followers of Goethe developed comparative plant morphology in that spirit. Such were the first conceptions of the phytonic theory, according to which the higher plant is an aggregate of individual foliar units, or phytons (French scientist C. Gaudichaud-Beaupré 1841; German scientist K. Schultze, 1843), as well as the theory of the three primordially existing “ideal” fundamental plant organs (German botanist A. Braun, 1850’s).

Plant morphology developed further in the first half of the 19th century. Independently of Goethe, A. P. De Candolle (1827) arrived at the concept of the equality of organs and their metamorphoses. R. Brown, the first to study the ovule in gymnosperms and angiosperms, discovered archegonia and spermatozoids in conifers. Braun, who studied metamorphosed organs and formulated, together with K. Schimper, the theory of the mathematical principles of phyllotaxy, played an important role in the development of comparative plant morphology.

The bases of ontogenetic and phylogenetic plant morphology were established in the first half of the 19th century. The German botanist M. Schleiden (1842–48) was an active proponent of the ontogenetic method. Phylogenetic plant morphology was introduced by the German botanist W. Hofmeister (1849–51), who described alternation of generations and proved the homology of the reproductive organs of Lycopodiales, Filicales, and Gymnospermae. As a result of this work it was possible to establish the morphological, and later the evolutionary, connection between spore and seed plants.

In the late 19th century and early 20th, C. Darwin’s evolutionary theory greatly influenced the development of plant morphology. Evolutionary, or phylogenetic, plant morphology was further developed by the Russian botanists I. D. Chistiakov and I. N. Gorozhankin (and his school) and the German botanists N. Pringsheim and E. Strasburger. These men demonstrated the homology of the reproductive organs of various plant groups and of the cycles of their development. Of particular value were Gorozhankin’s studies on the development of the gametophyte and on fertilization in gymnosperms, V. I. Beliaev’s investigations of the development of the male gametophyte in hetero-spores, and S. G. Navashin’s discovery in 1898 of double fertilization in flowering plants. The work of the Czech botanists L. Čelakovský (1897–1903) and J. Velenovský (1905–13) was also of great importance.

Another trend in evolutionary plant morphology was based primarily on the study of fossil plants. The British botanist F. Bower (1890–1908, 1935), the German H. Potonié (1895–1912), and the Frenchman O. Lignier (1913–14) shed some light on the cardinal problems concerning the origin of the principal organs of higher terrestrial plants. These scientists showed two possible paths for the origin of cormophytic structures; (1) the formation of surface lateral outgrowths (enations) on the primary leafless axis and (2) differentiation of the primary system of branching cylindrical homogeneous organs, in which there occurred a flattening and concrescence of parts of branches, with the formation of large, flat leaves. These formulations predicted the structure of the most ancient terrestrial plants—psilophytes—which were not discovered until 1917. The ideas of Bower, Potonié, and Lignier served as the basis for the telome theory formulated in 1930 by the German botanist W. Zimmerman.

The stelar theory of evolution, which was based on the taxonomy of higher plants proposed by the French botanist P. van Tieghem (1870’s) and developed by the American E. Jeffrey (1897) and his school, played a large role in the development of plant morphology. Some morphologists continued to develop the phytonic theory of the structure of plant bodies, which acquired a materialist and dynamic character (the American botanist Asa Gray, the Italian F. Delpino, the Czech Velenovský, the Russian A. N. Beketov, and the Frenchman G. Chauveaud). The subsequent reinterpretation of the concept of the phyton as a segment of a highly differentiated shoot-organ led to the purely ontogenetic view of the phyton as a unit of growth (British botanist J. Priestly, 1930’s; Swiss botanist O. Schuepp, 1938; Soviet botanist D. A. Sabinin, 1963).

Theories concerning flower origin constituted important achievements in evolutionary plant morphology. The British botanists E. A. N. Arber and J. Parkin formulated the strobilar theory of plant origin in 1907. The pseudantic theory of flower origin was proposed by the Austrian botanist R. von Wettstein in 1908. The Russian botanist Kh. la. Gobi published the first evolutionary classification of fruits in 1921.

Ontogenetic plant morphology in the post-Darwinian period developed closely with phylogenetic and experimental plant morphology. The German botanist A. Eichler studied the history of the development of the leaf (1869), as well as the structural principles of the flower (1878–82). The Russian botanist V. A. Deinega studied leaf ontogeny in monocotyledons and dicotyledons (1902). Highly metamorphosed plant forms were studied by the ontogenetic method by the Russian morphologists N. N. Kaufman (cacti, 1862), F. M. Kamenskii (bladderworts, 1877 and 1886), and S. I. Rostovtsev (duckweeds, 1902).

Beketov, who considered the physiological functions of plant organs and the effects of external conditions to be the most important factors in form development, made a major contribution to the development of experimental plant morphology (a phrase proposed by K. A. Timiriazev in 1890). The Russian botanist N. F. Levakovskii was one of the first to study experimentally the behavior of the shoots of a terrestrial plant in an aquatic medium (1863). The German physiologist H. Vöchting observed the influence of various natural conditions on form and discovered experimentally the phenomenon of polarity in plants (1878–82). The German botanists G. Klebs (1903) and K. von Goebel (1908) showed experimentally the dependence of the forms of organ growth on such factors as light, moisture, and food, and they induced artificial metamorphoses. Goebel was the author of the multivolume The Organography of Plants (1891–1908), in which he described the ontogeny of organs, taking into account external conditions and giving experimental verification of the causes of form development. The Austrian botanist J. Wiesner (1874–89, 1902) and the Czech R. Dostal (a series of works on experimental shoot formation, from 1912) did valuable research in experimental plant morphology. The Soviet botanist N. P. Krenke (1928, 1950) studied plant regeneration and the regularities of morphological changes that occur as a shootages, and he formulated a theory of the “cyclic aging and rejuvenation” of plants (1940).

Ecological plant morphology originated at the same time as phytogeography and ecology. One of its basic concerns is the study of the life forms of plants. The founders of this branch of morphology were the Danes J. E. Warming (1902–16) and K. Raunkiaer (1905–07) and the German botanist A. Schimper (1898). Russian and Soviet botanical geographers and geobotanists studied in depth the features of adaptive structures and methods of regeneration and reproduction of plants in various botanical-geographical zones and regions (A. N. Krasnov, 1888; D. E. lanishevskii, 1907–12, 1934; G. N. Vysotskii, 1915, 1922–28; L. I. Kazakevich, 1922; B. A. Keller, 1923–33; V. N. Sukachev, 1928–38; E. P. Korovin, 1934–35; V. V. Alekhin, 1936).

Current problems and trends Descriptive plant morphology is important in modern taxonomy in the compilation of floras, keys, atlases, and other reference materials. Comparative morphology is represented by the work of W. Troll (Federal Republic of Germany) and his school. Troll is the author of a fundamental survey on the comparative morphology of higher plants (1935–39), a number of teaching manuals, and a multivolume work on the morphology of inflorescences (1959–64). The British botanist A. Arber, in a discussion of comparative morphological data, arrived at a unique theory of the origin of the leaf as an “incomplete shoot”; this theory is closely related to the telome theory.

In 1952 the Soviet botanist I. G. Serebriakov investigated the comparative morphology of the vegetative organs of higher plants on an ontogenetic and phylogenetic basis. The Soviet botanists N. N. Kaden (from 1947) and R. E. Levina (from 1956) wrote works on the structure and classification of fruits. Evolutionary plant morphology was enriched by a new series of works by Zimmerman (1950–65), who further developed the telome theory he had formulated and showed the intimate connection of phylogenetic “elementary processes” and ontogeny. The Soviet botanist K. I. Meier summarized the study of the evolution of the gametophyte and the sporophyte of higher spore-forming plants and their organs (1958). He emphasizes the value of the comparative-morphogenetic method—the juxtaposition of the morphological structures of extant plants from groups that differ in their evolutionary levels and the construction of morphogenetic series that are not ancestor-descendant series but demonstrate the possible paths of the transformation of any given organ.

The problems of the morphological evolution of angiosperms are being studied by the Soviet botanist A. L. Takhtadzhian, who is working on the interrelationship of ontogeny and phylogeny and is developing in botany A. N. Severtsov’s concepts concerning the modes of morphological evolution. The Soviet botanist B. M. Kozo-Polianskii has written a series of works on the evolution of the flower and the monograph Basic Biogenetic Law From the Botanical Point of View (1937). A summary of the evolutionary morphology of flowering plants was published in 1961 by the American scientist A. Eames. The telome theory continued to be studied by the French scientists P. Bertrand (1947) and L. Emberger (1950–64). Many proponents of the telome theory have expressed contradictory views concerning the origin of the flower. In the 1940’s and 1950’s an argument flared up between the proponents of the classical strobilar theory of the origin of the flower (Eames, Takhtadzhian, the British botanist E. Corner) and the representatives of the “new” telome morphology. As a result of this discussion, extreme views were subjected to sharp criticism, and the positive aspects of telome theory, which convincingly portrays the course of the evolution of vegetative organs, were clearly expressed. Much study was devoted to the origins of the unique morphological features of monocotyledons, including Gramineae (A. Arber, Eames, M. S. lakovlev, Meier, L. V. Kudriashov, H. Jacques-Félix).

The ontogenetic trend in morphology has merged to a considerable extent with the experimental, and it is being intensively developed in connection with plant physiology (morphogenesis). In 1960 an extensive study on morphogenesis was published by the American biologist E. Sinnott. Particularly numerous are series of works studying shoot and root apexes as the fundamental sources of organogenesis and histogenesis in higher plants. Important theoretical proposals in the field have been made by the Swiss scientist Schüepp (1938), the Americans A. Foster (and his colleagues, 1936–54) and K. Esau (1960–65), the German H. von Guttenberg (1960–61), and the British botanist F. Clowes (1961).

The principles governing the activity of the shoot apex in connection with the general problems of the organization and evolution of plants have been studied by the British botanist C. Wardlaw and his school (1952–69). In France a new ontogenetic theory of leaf arrangement formulated by L. Plantefol (1947) and the investigations of R. Buvat (1950’s) have greatly influenced morphological study. In a number of universities in France and in the scientific center at Orsay (R. Nozerand), laboratories of experimental plant morphology are conducting valuable research. The work of E. Bunning (Federal Republic of Germany) is devoted to endogenic rhythms of morphogenesis.

In the USSR the most important work in morphogenesis has been conducted since the 1940’s by V. K. Vasilevskaia and her colleagues. Using a broad application of anatomic methods, they predominantly studied plants that live under severe ecological conditions. Since the 1950’s, F. M. Kuperman and his colleagues have studied the stages of organogenesis and their dependence on external conditions. V. V. Skripchinskii and his colleagues have studied the morphogenesis of herbaceous plants, particularly geophytes. Closely related to morphogenetic studies is the work of the physiologists D. A. Sabinin (1957, 1963) and V. O. Kazarian (since 1952). The work of N. V. Pervukhina, M. S. lakovlev, M. I. Savchenko, and M. F. Danilova is devoted primarily to the morphogenesis of flowers and fruits. A series of works by I. G. Serebriakov and and his school (1947) was devoted to morphological aspects of shoot formation and to the rhythms of the seasonal development of plants in various zones of the USSR. The morphological changes that occur when plants go through a lengthy life cycle are being studied, on the basis of the age periodization described by T. A. Rabotnov (1950), by his pupils and associates of I. G. Serebriakov and A. A. Uranov.

Ecological plant morphology is developing along the lines of further regional description and classification of life forms of plants. Comprehensive study is being conducted on the adaptability of plant forms to extreme conditions in the Pamir (I. A. Raikova, A. P. Steshenko); in the steppes, deserts, and mountain regions of Kazakhstan and Middle Asia (E. P. Korovin, M.Kul’-tiasov, E. M. Lavrenko, N. T. Nechaeva); and in tundras and forest-tundras (B. A. Tikhomirov and associates). Problems of classification and evolution of life forms were comprehensively elaborated by I. G. Serebriakov (1952–64), who designated the main course of morphological evolution from arborescent plants to herbaceous ones as the reduction of the life-span of terrestrial skeletal axes. His school is conducting research on the evolutionary paths of life forms in specific taxonomic groups; this promising direction is also being developed by the school of the German botanist H. Meisel (German Democratic Republic). V. N. Golubev (1957) also did work in this field. An important basis for evaluating the general directions of the evolution of life forms was offered in papers by Corner (1949–55) and the Swiss E. Schmid (1956, 1963).

Significance to the national economy The data of comparative, ecological, and experimental plant morphology makes possible an understanding not only of the principles of form development but of their practical application. Research on ontomorphogenesis and ecological plant morphology is important for working out the biological bases of forestry and grassland management, methods of raising ornamental plants, and recommendations for the rational use of beneficial wild plants (such as medicinal plants) and for their regrowth. This research is also important in the biological control of cultivated plants. The introduction of new species in botanical gardens is based on the data of ontogenetic and ecological plant morphology and, at the same time yields material for new theoretical generalizations.

Congresses, conventions, and publications Problems of plant morphology have been frequently discussed at international botanical congresses, particularly at the fifth (London, 1930), eighth (Paris, 1954), and ninth (Montreal, 1959), congresses. International symposia on certain problems are also held (for example, the symposium in London in 1956 on leaf growth). Colloquiums on plant morphology take place regularly in France (for example, on the structure of inflorescences, Paris, 1964; on life forms, Montpellier, 1965; on general problems of structural organization, Clermont-Ferrand, 1969; and on branching, Dijon, 1970). In the USSR problems of plant morphology have been discussed at conventions of the Botanical Society, at the All-Union Conference on Morphogenesis (Moscow, 1959), and at the All-Union Conference of Higher Educational Institutions on Plant Morphology (Moscow, 1968).

Papers on plant morphology are published in the international journal Phytomorphology (New Delhi, 1951). In the USSR the Botanical Institute of the Academy of Sciences of the USSR has published collections of works in the series Morfologiia i anatomiia rastenii regularly since 1950. Articles on morphology appear in Botanicheskii zhurnal (since 1916), Biulleten’ Moskovskogo obshchestva ispytatelei prirody (since 1829), Nauchnye doklady vysshei shkoly (since 1958), and other biological journals.

REFERENCES

Komarnitskii, N. A. “Morfologiia rastenii.’” In Ocherkipo istorii russkoi botaniki. Moscow, 1947.
Serebriakov, I. G. Morfologiia vegetativnykh organov vysshikh rastenii. Moscow, 1952.
Goethe, J. W. Izbr. soch. po estestvoznaniiu. Moscow, 1957. (Translated [from German].)
Meir, K. I. Morfogeniia vysshikh rastenii. Moscow, 1958.
Fedorov, A. A., M. E. Kirpichnikov, and Z. T. Artiushenko. Atlas po opisaternoi morfologii vysshikh rastenii. vols. 1–2. Moscow, 1956–62.
Serebriakov, I. G. Ekologicheskaia morfologiia rastenii. Moscow, 1962.
Eames, A. D. Morfologiia tsvetkovykh rastenii. Moscow, 1964. (Translated from English.)
Takhtadzhian, A. L. Osnovy evoliutsionnoi morfologii pokrytosemennykh. Moscow-Leningrad, 1964.
Takhtadzhian, A. L. Proiskhozhdenie i rasselenie tsvetkovykh rastenii. Leningrad, 1970.
Goebel, K. von. Organographie der Pflanzen, parts 1–2. Jena, 1928–33.
Troll, W. Vergleichende Morphologie der höheren Pflanzen. vols. 1–2. Berlin, 1935–39.
Troll, W. Praktische Einführung in die Pflanzenmorphologie, parts 1–2. Jena, 1954–57.
Wardlaw, C. Organization and Evolution in Plants. London, 1965.

T. I. SEREBRIAKOVA

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