THE COMPARATIVE ANATOMY OF THE SECONDARY XYLEM AND THE PHYLOGENY OF THE EUCOMMIACEAE

IN 1921 Parkin, discussing the systematic position of Eucommia, wrote: "This tree might repay further study from the anatomical side. The wood especially requires minute examination. Facts might possibly be forthcoming which would throw light on its relationship." The present writer (1938) came to the same conclusion in the course of an investigation dealing with the comparative anatomy of the Moraceae and their immediate allies. A cursory survey of the anatomy of the Eucommiaceae indicated that this family might form a connecting link between the Urticales and the Hamamelidales. Unfortunately, at that time but one young specimen of Eucommia was available to the writer. Therefore, the present study, based on mature and abundant material, was undertaken to supplement the earlier investigation. The family Eucommiaceae Van Tieghem consists of the single genus Eucommia which, in turn, contains but one species,2 Eucommia ulmoides Oliver. This species is a native of the mountains of Central China but is widely cultivated in Europe (W. W., 1903; Mottet, 1909; Kache, 1912; and Purpus, 1917) and in the United States, for it is hardy as far north as Massachusetts. Recently, Hanley (1937) described the qualities which make this plant a very desirable ornamental. The plant is of additional interest for it is the only hardy rubber-bearing tree in temperate regions. Unfortunately, the percentage of latex is small and it is difficult to extract, both because it is hard to separate from other materials and because the caoutchouc is dry and will not flow from the plant (Parkin, 1921; Weiss, 1906-07). DESCRIPTION OF THE EXTERNAL MORPHOLOGY.Eucommia ulmoides is a deciduous tree attaining, occasionally, the height of sixty feet and a girth of five feet. Its general growth habit suggests that of some of the elms. Eucommia is dioecious and the flowers lack a perianth. The male flowers occur in clusters. The individual male flowers are stalked and consist of a group of 4 to 10 stamens which dehisce longitudinally. The female flowers are borne in solitary fashion in'the axils of bracts. The individual female flowers are stalked and consist of two fused carpels, one of which aborts. There are two stigmas and two anatropous ovules which are pendulous from the top of the ovary. One of these ovules usually aborts. The fruit is a samara which is similar to that 1 Received for publication July 24, 1940. The writer wishes to express his gratitude to Professor R. H. Wetmore of Harvard University and to Professor S. J. Record of Yale University, both of whom supplied wood samples; to Carl Withner who prepared some of the slides; and to Dr. Majel MacMasters who assisted with some of the photomicrographs. 2 Leveille (1916) named a Eucommia ulmoidea (his misspelling) Oliv. var. yunnanensis Liveille, but Rehder (1936) states that it is just like the type and therefore the varietal name is invalid. of the elm. The seed contains a large embryo surrounded by copious endosperm. The leaves are alternate, simple, petioled, serrate, and pinnately veined. They resemble elm leaves except that there are no stipules. Latex cells are present in the leaves and in the pith and bark of the stem. SYSTEMATIC POSITION OF THE FAMILY.-The plant now called Eucommia, was known to the Chinese, by whom the medicinal qualities of the bark were (and are) much esteemed, long before it was studied taxonomically and given its scientific name. Wilson (1913) reports that the bark, referred to as Tu chung or Tsze-mien by the Chinese, is used by them as a tonic, diuretic, and aphrodisiac. Parkin (1921) states that it is also employed as a cure for hepatic diseases and arthritis. Whether the tree contains any principle of therapeutic value is doubtful, but it is a fact that the bark is described in nearly all Chinese works on materia medica. The earliest mention, according to the Kew Bulletin (1904), is in an herbal of which Emperor Shen-Nung is the reputed author. This herbal was probably written as early as the twenty-eighth century B. C. The bark of Tu chung was known in European countries long before the plant was named scientifically. For example, the Kew Report of 1881 (Kew Bulletin, 1901) refers to it. The botanical origin of the bark was not known, although suggestions (Holmes, 1891) were made to the effect that it might have been derived from Euonymus, Parameria, and still other genera. In 1890, Professor Daniel Oliver described some specimens received from Dr. A. Henry of China. Oliver named the plant Eucommia ulmoides, but since the specimens lacked flowers, he made no real attempt to assign the plant to a systematic position. He did, however, suggest that since latex was present, the plant might belong to the tribe Phyllantheae of the Euphorbiaceae. He also pointed out that the general habit and the samaroid fruit suggested the Ulmaceae and hence he gave the plant the specific name ulmoides. In 1895, Oliver described and figured specimens with flowers. He put the genus in he Trochodendraceae. Solereder (1899) assigned the genus Eucommia to a special tribe of the Hamamelidaceae. He pointed out that the gynoecium did not consist of one carpel as Oliver had stated, at least in one place (1895), but was made up of two fused carpels. Van Tieghem (1900) established the family Eucommiaceae but did not indicate its affinities. In the first edition of Engler and Prantl's "Die niiturlichen Pflanzenfamilien," Harms (1897) classified Eucommia in the Trochodendraceae of the Magnoliales. Later, he (1908) followed Van Tieghem and placed the genus in its own family, the Eucommiaceae. In the second edition of "Die niiturlichen Pflanzenfamilien." Harms (1930) deposited