THE SIGNIFICANCE OF WOOD ANATOMY IN THE TAXONOMY OF THE JUGLANDACEAE

MANNING (1938a) has recently made a comparative morphological investigation of inflorescences of the various members of the Juglandaceae. He finds that the inflorescences of the family are based on a fundamental pattern though showing varying degrees of reduction along certain definite lines from a primitive type. This primitive type is a terminal androgynous panicle consisting of a central pistillate catkin surrounded by several staminate branches or catkins. In Manning's opinion, the genera Alfaroa, Engelhardtia, and Platyearya exhibit this primitive type, whereas the genera Juglans, Carya, and Pterocarya possess specialized or derived types of inflorescences. His conclusions were founded on morphological rather than anatomical considerations. That studies of the secondary xylem in the dicotyledons may aid the phylogenist in his attempts to establish natural relationships among certain families of Angiosperms has been shown by Vestal (1937), Tippo (1938), and Taylor (1938), students from these laboratories. In these investigations involving taxonomic groupings of families attempts were made to correlate xylem structure with existing systems of classification, and their findings indicate an interestingly high degree of correlation between the two. So much is this the case that groups which fail to show this correlation are suspected of being erroneously placed in the system being examined. Bailey and his students have established certain lines of structural specialization in dicotyledonous xylem. Bailey and Tupper (1918) obtained significant data regarding the classification and length of vascular elements. Frost (1930a, 1930b, 1931), by statistical methods, after a survey involving the majority of the dicotyledonous families, revealed the trends of specialization of the vessel segment. Using Frost's results as a basis, Kribs (1935) found a high degree of statistical correlation between the type of wood rays and the degree of specialization in the vessel segment. By use of similar methods, Kribs (1937) correlated vertical parenchyma patterns with primitive and advanced types of vessel members. Although the previous attempts to use these anatomical tools have had as their central theme the determination of relative positions of families in natural taxonomic groupings, evidence was also obtained that these anatomical principles would apply equally well to considerations within the specific family, providing a significant range of structural variability exists in the family. A detailed description of the anatomy of the secondary xylem of the Juglandaceae was published bv Kribs in 1927, based on the limited material available to him. With these lines of specialization in mind, and a fairly complete representation of the 1 Received for publication June 19, 1939. genera with which to work, the present investigation was undertaken in order to determine to what extent the findings based on xylem anatomy of the Juglandaceae would accord with those obtained from a study of the organization of the inflorescences. MATERIALS AND METHODS.-For this investigation the microscopic slides, the dried, and the preserved wood in the Harvard Collection were at the writers' disposal. Through the courtesy of Professor Samuel J. Record of the Yale School of Forestry, additional specimens were obtained. Material was also collected from members of the family growing in the Arnold Arboretum. Before additional slides were made, it was found necessary to soften the material in hydrofluoric acid. When embedding was necessary, celloidin was used, following the standard technique of Wetmore (1932). The living material was fixed in formacetic-alcohol, washed in tap water, softened and embedded. Sections 10 micra thick were made, stained with safranin and Heidenhain's iron-alumhaematoxylin, and mounted permanently in Canada balsam or diaphane. Macerations were made of representative material of all the genera, using equal amounts of 10 per cent chromic and 10 per cent nitric acids at a temperature of 60?C. for 48 hours. Following thorough washing, the separated elements were stained with water-soluble nigrosine and dehydrated in rapidly increasing percentages of ethyl alcohol. Permanent mounts were made using diaphane as a mounting medium. Preliminary examinations showed that when 50 measurements of the vessel member lengths and of fiber-tracheid lengths were used, these followed the normal curve of distribution; thus, this number of length measurements was averaged for the respective elements for each species. From these the averages for the genera were derived. For vessel diameters 25 random measurements were averaged for each species represented, except for those species which were ring-porous or tended toward ring-porosity, then only the larger pores were measured. The values for the angle of the end wall were obtained by taking 10 random measurements of each species with a camera-lucida. These were averaged, and from these the averages for the genera were computed. Preliminary figures concerning ray height were not significant, and this can be attributed to ontogenetic changes in the form and character of the wood rays. With increased knowledge concerning the ontogeny of the various types of wood rays, statistical treatment of the characters may prove to be significant. All photographs were taken on DC Ortho plates with Zeiss lenses and Zeiss photomicrographic equipment.