Phytonic Theory

a concept in plant morphology that holds that the basic structural element of the plant is the phyton (phytomer, anaphyte, meriphyte, phyllorhiza), which consists of a leaf with the associated portion of the stem (the node and the internode below it). The phyton also includes the axillary bud and the adventitious root, which potentially may form on any part of the plant.

The basic principles of phytonic theory were advanced by the German poet and naturalist J. W. von Goethe, who stated in his Essay on the Metamorphosis of Plants (1790) that all organs of a plant are metamorphoses of the leaf (type-leaf). The founders of phytonic theory were the French scientist C. Gaudichaud-Beaupré (1841) and the German scientist K. Schulze (1843). Several variations on the theory were later developed by such major botanists as the American Asa Gray (1879), the Italian F. Delpino (1883), the Russian A. N. Beketov (1897), the Czechs Celakovsky (1901) and J. Velenovsky (1905), the Frenchman G. Chauveaud (1921), the British botanist J. Priestley (1931), and the Swiss scientist O. Schiiepp (1938).

Phytonic theory reflects the metameric structure of the shoot in higher plants and the decisive influence of the leaf on the formation of the stem, in particular its stele, the central part of the vascular system. The development of the shoot in ontogeny corresponds fully to phytonic theory, inasmuch as the leaf rudiments and their nodes take shape first on the growing point, while the internodes proliferate later by means of intercalary growth; this is especially evident in grasses. In the ontogeny of certain ferns, the formation of successive phytons (phyllorhizae) can be precisely traced.

In phylogeny, however, phytonic theory is unacceptable and has on several occasions been justifiably criticized, for example, by the German scientist G. Krüger (1851), the British scientist F. Bower (1890, 1908), and the Soviet scientists B. M. Kozo-Polianskii (1937) and K. I. Meier (1946). From the evolutionary point of view, the leaf cannot be regarded as the parent organ of all higher plants. The first terrestrial flora had no leaves, and the development of leaf and stem structures proceeded by various means.