THE MORPHOLOGY OF THE BUD AND THE DEVELOPMENT OF THE LEAVES OF VIBURNUM RUFIDULUM

Abstract

THE RAPIDLY increasing literature on the leaf and bud has been reviewed recently by Foster (1936a, 1928), Avery (1933), Schuiepp (1929), Zimmerman (1928), and others. The need for additional information is apparent to most workers, but there is some difference of opinion concerning the relative values of the various methods of study. Troll (1935) thought that ontogenetic studies are of relatively little valuethat the comparative study of a wide range of adult forms (typological method) is of greater importance. On the other hand, Foster (1936a) pointed out that in developing our knowledge of the leaf it would seem obvious that a sound and well balanced morphological treatment must attempt to relate the facts of development impartially to the form and structure of the adult organ. The typological method as an approach to the problem of foliar morphology is useful, but it seems that conclusions based upon such studies can hardly be considered trustworthy until comparative data concerning the growth processes of organs are assembled and correlated with the comparative studies of adult form. The value of a knowledge of the various histogenetic processes that occur in a leaf was recognized as early as 1872 by Lund, whose neglected monograph has been brought to the attention of modern workers (Foster, 1936b); and among recent investigators histogenetic studies have been and are being increasingly used in the interpretation of floral structures (Gregoire, 1935c; Newman, 1936). This report deals with the morphology of the bud and with the developmental behavior of the leaves of Viburnum rufidulum Raf., particularly with respect to the type, origin, and duration of meristems. The genus Viburnum (Tourn.) L. provides a good source of material for comparative foliar studies. Among the various species are some with highly specialized cataphylls (V. Opuluis L.), some with cataphylls lacking (V. Lantana L.), and others which seem to represent a position intermediate between these two extremes (V. rufidulum Raf., V. Lentago L.). Some species (V. Opulus) have lobed leaves with stipular appendages, others have leaves with entire margins and stipular appendages lacking. While this study will deal only with the structure and development of the foliar organs of Viburnum rufidulum, it is hoped that comparative studies can be made at an early date with V. Opulus (highly specialized cataphylls) and V. Lantana (naked buds). The researches of Cross (1937), Foster (1935a), and Schiiepp (1929) show that in some cases the foliar organs of plants with highly specialized cataphylls