Contribution of Eminent Scientists Towards Plant Anatomy

The below mentioned article provides an overview on the contribution of eminent scientists towards plant anatomy.

The word anatomy has derived its origin from ana, meaning asunder, and temnein, meaning—to cut. So it is regarded as the branch of botany which considers the internal structures and organization of the plant members. It is also known as internal morphology.

Unfortunately the term histology (histos=cobweb) is used as a synonym for ana­tomy.

Histology deals with the minute internal structures like cellular arrangements, tissues and tissue systems; but gross internal structures like steles, vascular skeleton, leaf- trace and branch-trace systems do not come under histology.

Specialised study of the cell belongs to cytology which is now treated as an independent branch of biology. Ana­tomy is really concerned with both minute and gross internal structures. Thus histology is covered by anatomy.

There is no denying of the fact that anatomy is rather a recent branch in comparison to morphology and taxonomy. Though really serious studies on anatomy started with the invention of the microscope in the later part of the sixteenth century, but this branch had also its beginning. Long before Christ and Greek Civilization ancient Hindus of India devoted their attention to the subject.

They distinguished five regions in the body of the plants, viz. tvac (skin), mansa (soft tissues or bast), asthi (wood or bone), majja (pith), and snayu (fibres in the bast).

Mansa was further divided into valkala (bark) and sakara (bast fibres). History of biological studies is usually traced from the time of great Aristotle (Fig. 473) of Greece who lived in the fourth century B.C. Theophrastus (Fig. 474), a pupil of Aristotle, is credited for his work on internal structure of plants.

He said—”plants are made of phloios (bark), zylon (wood) and metra (pith), when pith is present”. Thus the very commonly used terms xylem and phloem were coined by Theophrastus.

He worked on the anatomical problems rather extensively, of course with the limited and meagre re­sources at his disposal. He is thus regarded as the father of botanical science as regards anatomy in particular.

Since then for a pretty long time there was nothing noteworthy in anatomical work due to the want of a magnifying apparatus, though considerable ad­vances were made in other branches like morphology and more so in applied sciences like medicine and agriculture.

Real interest re-awakened with the invention of the microscope. The first compound microscope was produced in about 1590 by Dutch spectacle makers, Jans and Zacharius Janssen.

During the first part of the seventeenth century more improved models were designed. This wonderful instrument aroused curiosity in the workers and led to many significant discoveries. Robert Hooke (1635-1703) in England examined a piece of bottle cork under a microscope (front piece of this part) improved by himself which looks like a fire-extinguisher to twentieth century eyes, and noted the cells.

His observations were published in Micrographia in 1665. Curiously enough the credit of such an important discovery goes to Hooke, who was for some time a collaborator of Robert Boyle, curator and later Secretary of the Royal Society, but not a student of biological science.

It is sug­gested in some quarters that Hooke probably used his tool more as a play-thing than as something for serious scientific pursuit. Nehemiah Grew (1641-1712, Fig. 475), an Eng­lish physician and Marcello Malphigi (1628-94, Fig. 476), an Italian physician and pro­fessor, independently carried on very useful works on internal structures, though the approach of both of them; being physicians themselves, had been mainly from the point of view of medicine.

Grew published his work in 1682 under the title—The Anatomy of Plants, where he discussed the gross structures of plants, and compared the vascular skele­ton of the plants with that of the animals. The commonly used terms of anatomy like parenchyma, vessels, cortex, etc. were introduced by him. Malphigi’s investigations were -more or less in the same line.

He discovered the spiral vessels and the stomata. His pio­neering works on vascular plants came out in his ‘Anatome Plantarum’ in 1675. Both Grew and Malphigi made attempts to relate the anatomical structures with their physio­logical functions.

So spectacular progress made in the seventeenth century practically waned in the next century. Again in the nineteenth century works on anatomy started with fresh energy by Charles Francois Mirbel (1776-1854), Kurt Sprengel (1766-1833) and Others.

These scientists primarily worked on the origin of the cells. The method of formation of a vessel from a series of Cells became more clear. Nucleus was first discovered by Robert Brown (1773-1858) in the skin of orchid leaves.

Though some earlier workers noted this centrally located body in the cell, they failed to recognise its importance. Till this time nobody could unravel the mystery of proto­plasm.

Suggestions had been put forward by many workers as regards the existence of the living contents of the cells, and different names like nourishing juice, ‘sarcode’, etc. were pro­posed, but the nature of the mysterious fluid remained practically unknown.

Hugo von Mohl (1805-‘72, Fig. 477) was the first man to recog­nise the importance of protoplasm and was instrumental for shifting the attention of the workers to the contents from the wall.

The conception of a cell became clearer; and that it is essentially a mass of protoplasm with its outer secretory product, the cell wall or without it, holds good even now.

Matthias Jacob Schleiden (1804-‘81, Fig. 478), a botanist, and Theodore Schwann (1810-‘82, Fig. 478), a zoologist, worked on plant and animal tissues respectively and postulated a theory known as Cell

theory or Cell doctrine in 1838.

The Cell theory demands that all living things are essentially cellular in nature. Thus they defined the basic unit of life.

Hugo von Mohl, apart from putting the cell theory on a solid foundation, carried on extensive investiga­tions on plant anatomy, viz., nature and formation of vessels, structure of epidermis, lenticel and cork and bark; and also traced the course of vascular bundles in stems and leaves.

He carried his work with so much of accuracy and thoroughness that a new epoch was opened in plant anatomy. Rudolf Virchow, a great German physician, asserted that cells originate only from pre-existing cells.

Carl von Nageli (1817-,’91, Fig. 479) was another contemporary worker who made very valuable contribution to anatomical studies.

Nageli’s works were particularly con­fined to ontogenetical studies—on primary and secondary meristem, the types of vascular bundles—common, cauline and foliar bundles.

Nageli was really the originator of the terms xylem and phloem, as we understand them today. It can be said that after Robert Hooke’s discovery of cells, Grew and Malphigi laid the foundation of plant anatomy, and Hugo von Mohl and Carl von Nageli developed its super­structure; so that they may be called the foun­ders of modern plant anatomy.

Edward Strasburger could describe the chromosomes and their behaviour during cell division using Abbe microscopes, which were available then, and basic Aniline dyes. Spetacular advances were made in the studies of the structures and forms of Plant tissues. Cytoplasmic and nuclear structures were naturally much better under­stood.

In the modern period studies on the meristems and zonation of tissues at the root- and stem-apices gained prominence. Hanstein postulated the ‘histogen theory’, asserting that three histogens or tissue-builders occur at the tips, which in course of time develop into the three tissue-systems.

Julian von Sachs (1832-’97) first introduced that there are three tissue-systems in plants. Increasingly more emphasis was being laid to the physiolo­gical aspect, rather than morphological, what early workers did, of anatomy.

Simon Schwendener (1829-1919) and more particularly the great Gottileb Haberlandt were the exponents of this approach. Haberlandt published the results of his work in his classical book ‘Physiological Plant Anatomy’.

According to his own statement ‘homologies of the tissues were of no interest to him’ and that he was ‘solely concerned with analogy’. He put the tissues into twelve systems, viz., dermal system, absorbing system, etc. purely on the basis of function.

Without in any way underestimating Haberlandt’s great contribution, it should be said that physiological anatomy is really of value to the physiologist, rather than to the anatomist, because origin, contiguity, topography and phylogeny of the tissues were rather ignored in these systems.

Anton de Bary (1831-88), primarily a student of fungi, worked on plant anatomy and presented the same in his book ‘Comparative Anatomy of Phanerogams and Ferns’ in 1877. Edward van Tieghem (1839-1914) made further improvement and established the stelar theory. In collaboration with his students Tieghem worked on the various types of steles and explained them on the basis of comparative morphology and phylogeny.

The contribution of Edward Charles Jeffrey towards knowledge of stele and stelar nature of vascular plants also merits special mention. Anatomical characters were being used in taxonomy more frequently than what found expression in the very important works— Engler and Prantl’s ‘Die Naturliche Pflanzenfamilien’ and Solereder’s ‘Comparative Anatomy of the Dicotyledons’.

In the recent years developmental plant anatomy has come to the forefront. Seve­ral investigators in different parts of the world are now engaged in searches cm the deve­lopmental history of the plants. Very valuable contributions on this aspect have been made by I. W. Bailey, A. S. Foster, K. Esaw, G. P. Majumder and Others.

Due to their very important and useful works the conceptions about meristems, the zonation and structural development, histogenesis of the organs—shoot, root and flower are becom­ing increasingly more clear. A very useful instrument microtome was devised in late nineteenth century and gradually improved models were available.

This tool has proved to be of inestimable value in studying developmental history of plant organs because serial sections of uniform thinness could be made. Fortunately modern workers have at their disposal more improved instruments and technical devices which would enable them to make spectacular advances in their search for truth.

Plant anatomy is an important basic science. For properly understanding the fascinating physiological processes going on inside the plant body and phylogenetic relationship existing between the various plant groups a thorough knowledge of anatomy essential.

Ecological adaptations to different’ environmental conditions can be more rationally interpreted in terms of their anatomical peculiarities.