Matthias Jakob Schleiden

1804-1881

German Botanist

Matthias Jakob Schleiden and Theodor Schwann (1810-1882) are generally regarded as the first scientists to establish cell theory. Cell theory is a fundamental aspect of modern biology. This powerful generalization has played an essential role in explaining the basic unity of plant and animal life, the mechanism of inheritance, fertilization, development and differentiation, and evolutionary theory. Building upon the discovery of the cell nucleus by Robert Brown (1773-1858), Schleiden demonstrated that plants are composed of cells and cell products.

Schleiden studied law at the University of Heidelberg, but he was so unsuccessful in his attempts to establish a law practice in Hamburg that he was driven to suicide. Fortunately, his self-inflicted gunshot wound was not fatal. By the time he had recovered from his injury and depression, Schleiden decided to give up law and study natural science. He earned doctorates in medicine and philosophy and was appointed professor of botany at the University of Jena. Despite his success in research and teaching, he suffered from nervousness, fatigue, and depression. He resigned after 12 years and decided to rest his nerves and to travel. During a visit to Berlin he met with Schwann and described his ideas about plant cells.

Contemporaries generally described Schleiden as arrogant and unsympathetic towards rivals and predecessors. However, Schleiden did accord considerable respect to the work of Charles Brisseau-Mirbel (1776-1854), an eminent French botanist and microscopist. Brisseau-Mirbel thought that cells were found in all parts of the plant. Schleiden generally agreed with Brisseau-Mirbel's suggestion that cells formed in some sort of primitive fermenting fluid.

Schleiden thought that most botanists were wasting their time arguing about old systems of taxonomy. He wanted to redefine botany as a new inductive science concerned with the forms and functions of the whole vegetable kingdom. He complained that botanists had discovered few facts and had established no new fundamental laws and principles. He believed that botanists should abandon systematic taxonomy and focus on the study of the chemistry, physiology, and microscopic structure of plants.

In 1838 Schleiden published his new ideas as "Contributions to Phytogenesis" in Müller's Archives for Anatomy and Physiology. Recognizing the importance of Robert Brown's discovery of the cell nucleus, Schleiden argued that the nucleus, which he renamed the cytoblast, was an essential component of all plant cells. He believed that all higher plants were aggregates of cells. The cells that made up the plant led a double life. In part they were independent entities, but they also served as integral parts of the plant. All aspects of plant physiology, therefore, resulted from the activity of the cells.

Although Schleiden described several possible methods of cell formation in "Contributions to Phytogenesis" and later in his major treatise Principles of Botany, he generally supported the hypothesis known as "free-cell formation." That is, he thought that cell growth was rather like the process of crystallization. Presumably, granules in the cytoblastema, a fluid containing sugars and mucus, aggregated to form a nucleolus. More granules joined those that made up the nucleolus until the cytoblast (nucleus) formed around the nucleolus. Eventually, a young cell developed around the mature cytoblast and the rigid plant cell wall formed around the new cell. Schleiden though it was also possible for cells to form within cells in the growing plant. The contents of such cells would divide into two or more parts and a membrane would separate each part. He suggested that wood was formed when materials in plant juices were quickly aggregated. Although the mechanism by which cells multiplied was unclear, Schleiden was quite opposed to the doctrine of spontaneous generation. He was convinced that even the simplest plants, such as algae, lichens, and fungi, arose from parents of the same kind, not from spontaneous generation out of nonliving substances. Schleiden's work was confined to the plant world, but it was his work on cell theory that stimulated Schwann's study of the role of the cell in animals.

LOIS N. MAGNER