Plant Anatomy

the branch of botany concerned with the internal structure of plants. Plant anatomy is a division of the more general botanical discipline of plant morphology as it is understood in the broad sense—that is, the study of the microscopic structure of plant tissues and organs. In its narrow sense, plant morphology studies only the external forms of plants and their organs. Plant anatomy is closely related to plant physiology, the science of the vital processes which take place in plants. Plant anatomy, in turn, has given rise to the independent science of cytology, which is the study of the cell, a rapidly developing field that plays a great role in the understanding of vital processes in general and of the phenomena of heredity and mutability in particular.

The emergence of the field of plant anatomy is closely related to the invention and perfection of the microscope. The English physicist R. Hooke observed in 1665 the cellular structure of thin slices of cork, elder pith, and wood from various plants, using a microscope of his own improved design. The real founders of plant anatomy, however, are considered to be the Italian biologist M. Malpighi and the English botanist N. Grew, who published the first (1675–79) and the second (1682) works on this subject; in these works the results of a systematic microscopic study of plant material were presented. Further development came only at the beginning of the 19th century. The German scientist J. Moldenhawer in 1812 and the French researcher R. Dutrochet in 1824 were able to divide plant tissue into its component cells through maceration (soaking). In 1831 the English botanist R. Brown observed the cell nucleus; this achievement, in combination with the studies of the German botanist M. Schleiden, played a great role in the founding of cellular theory, whose author was the German biologist T. Schwann (in 1839). After this time, increasing attention was devoted to the content of the plant cell,which the Czech scientist J. E. Purkin named “protoplasm” (1839–40). A number of the properties of protoplasm were studied and described by the German scientist H. Mohl in 1846. The German botanist G. Haberlandt applied the physiological principle in the study of plant structure. Great contributions to the field of plant anatomy were made by the French biologist P. Van Tieghem and the German biologists A. de Bary, C. Nägeli, K. Sanio, J. Hanstein, and S. Schwendener. A number of Russian botanists also contributed significantly to the advancement of plant anatomy—for example, I. V. Baranetskii, S. P. Kostychev, V. R. Zalenskii, V. F. Razdorskii, V. G. Aleksandrov, and O. N. Radkevich.

The elements of the plant cell are the membrane and the protoplast. The protoplast includes the cytoplasm, the nucleus, the plastids, the mitochondria, and other organelles. There are also the products of the vital activity of the protoplast—reserve materials, mineral deposits, resins, ether oils, and so forth. Complexes of a number of cells constitute plant tissues, which are classified on the basis of their origin, structure, or physiological role. There are meristematic (formative) tissues and permanent tissues, which develop from them. The most widely used system of tissue classification is based on the physiological role of the tissues. Plant tissues are classified as external, conducting, mechanical, nutritional, or one of a number of other types.

In the past, the chief objects of study in plant anatomy were the vegetative organs (stem, root, and leaf); today, attention is also given to the structure of flowers, fruits, and seeds. Within the field of plant anatomy are (1) physiological plant anatomy, which is concerned with the links existing between plant structure and internal processes; (2) ecological plant anatomy, which is the study of environmental effects on plant structure; (3) pathological plant anatony, which is the study of the effect of disease-producing agents of a biological, physical, and chemical character on plant structure; and (4) comparative, or systematic, plant anatomy, which introduces the comparative study of representatives of the different systematic groups (taxa)—species, genera, families, and so forth—for clarification of their phylogenetic bonds.

The basic method used in plant anatomy, or the study of internal plant structure, is the preparation of thin slices which are studied microscopically. From this the science “derives its name (in Greek, anatomë means “dissection”). New research techniques are in use as well—for example, polymerization; ultraviolet, luminescence, and phase-contrast methods; electron microscopy; histochemi-cal methods; and X-ray diffraction analysis. Anatomical research is carried out to answer questions regarding the origin of plants and to provide information about the effect of external conditions on various agricultural crops. Such research also helps to solve many problems in fields other than biology and agronomy, such as technology, the history of culture, criminology, and a number of branches of industry—food, furniture, pharmaceuticals, cellulose-paper production, and so forth. For example, plant anatomy offers a means of detecting the presence of impurities in flour through the use of microscopic study of starch grains; it can also be used to determine the species and condition of medicinal raw material. It also may help to resolve such economic problems as timber-cutting schedules (through the study of the structure of cambium and adjacent layers) and questions concerning the materials from which writing paper and other such articles of labor and daily life were manufactured in ancient times, which are important in the history of culture and technology.