STEM ANATOMY AND PHYLOGENY OF THE RHOIPTELEACEAE

THE FAMILY Rhoipteleaceae, from southwestern China and Tonking, was described by Handel-Mazzetti in 1932. At that time Handel-Mazzetti suggested that the family might belong to the Urticales or to the Juglandales. Wettstein (1935) includes the family in the Urticales, as do Engler and Diels (1936). Tang (1932) believes, on the basis of the anatomy of the wood, that the Rhoipteleaceae are more closely similar to the Ulmaceae than they are to the Juglandaceae. On the other hand, Tippo (1938) says, "The fact that the perforation plates are exclusively scalariform and that the vessel elements are so long makes it obvious that this family does not belong in the Urticales." He makes, however, no phylogenetic placement of the family. Accordingly, the purpose of the present study was to investigate more fully the stem anatomy of the Rhoipteleaceae with the hope that such a study might aid in determining the phylogenetic position of the family. MATERIALS AND METHODs.-Material from four specimens was available for this investigation: from the Yale University collection, No. 29795, sent by Tang; and from Harvard University, Nos. 23044 and 17766 (slides), both from material collected by Tsiang in Kweichow. Two-year-old twigs, H23762, with bark were also available and came from herbarium material in the Arnold Arboretum (Steward and Cheo, No. 70). The wood blocks were treated in the usual manner: boiled, softened in hydrofluoric acid, washed, dehydrated, and stored in glycerine-alcohol. The twigs were prepared according to the celloidin method described by Wetmore (1932). Cross, radial, and tangential sections of all specimens were cut with a Reichert sliding microtome and were stained with Heidenhain's iron-alum hematoxylin and safranin. Macerations were made with Jeffrey's maceration fluid (Chamberlain, 1932) to supply material for the measurements of cells. From the macerations of each specimen, the lengths of one hundred fiber-tracheids were measured, as were the total lengths (Chalk and Chattaway, 1934) of one hundred vessel elements. From sections, one hundred tangential vessel diameters were measured for each specimen. The appropriate calculations as suggested by Rendle and Clarke (1934a, 1934b) were made and are found in table 1. Since H23762 is immature wood, the results obtained from it were not averaged in the totals for the species. As pointed out by Tippo (1940), the measure1 Received for publication June 16, 1941. The author sincerely thanks Dr. Oswald Tippo of the University of Illinois for suggesting and supervising this problem, Professor S. J. Record of Yale University and Professor R. H. Wetmore of Harvard University for supplying the material used, and Dr. Neville Jones of the University of Illinois for criticism and advice on taxonomic matters. ments of vessel elements or fiber-tracheid lengths obtained from slides are not accurate, so only vessel diameters were measured for H17766. The terms used are those prescribed by the International Association of Wood Anatomists (1933). Kribs' (1935) ray classification was followed as was Tippo's (1941) list of diagnostic features for wood description. The terms of Chattaway (1932) for numerical values used in the description of wood were also used. Herbarium material kindly loaned by Dr. E. D. Merrill, Director of the Arnold Arboretum, was examined to study most of the characters of the external morphology. Five specimens in all stages of development were available. One (Tsiang, No. 6568) is an isotype and wood sample H17766 was taken from the same tree. DESCRIPTION OF THE EXTERNAL MORPHOLOGY.The Rhoipteleaceae (Handel-Mazzetti, 1932) consist of the single species, Rhoiptelea chiliantha Diels and Hand., an aromatic tree which attains a height of twenty meters. The imparipinnately compound, deciduous leaves are alternate and are thickly covered by a finely curved indument and many shieldshaped glands. Stipules are present. The inflorescences are large, nodding, terminal panicles. The flowers are grouped in threes; the laterals are female and usually aborted and the middle one is perfect. The three flowers are surrounded by a large unlobed bract and two bracteoles. Each of the small aborted female flowers has two small subtending bracts. The perianth is composed of four uninerved, scarious brown parts which persist under the fruit. A discus is absent. In the middle flower the six episepalous stamens are erect and persistent, their bisaccate anthers opening by longitudinal slits. The pollen grains are about 22 ,u in diameter, tetrahedric, with thickenings in the corners. The superior ovary is transversely biloculate; one locule is aborted and the other has a single, half-anatropous ovule affixed to the septum. The two stigma lobes are lamelliform and subrhombic, often being bior tricuspidate. There are two integuments. The fruit is a samara (5 to 8 mm. in diameter), the wings of which are four-nerved with a sinus at the apex. There is no endosperm, and the embryo is straight. Apparently the plant is windpollinated, as it has no nectaries or other devices which might attract insects. ANATOMICAL DESCRIPTION OF THE XYLEM.Growth rings are present in all specimens and range from 736 y to 3,015 [ in width (fig. 1, 6). The body of the xylem is composed of fiber-tracheids with minute bordered pits (1.5 to 1.9 I in diameter). The walls are usually thin but are thick in the case of the gelatinous fibers (fig. 1) which are present in H23044 and Y29795. Table 1 lists the range, the most frequent range, the mean, the standard deviation, and the standard errors for the lengths of one hundred fiber-tracheids of each specimen. The