1941] BAILEY & HOWARD, MORPHOLOGY OF THE ICACINACEAE 125THE COMPARATIVE MORPHOLOGY OF THE ICACINACEAE I. ANATOMY OF THE NODE AND INTERNODE I. W. BAILEY AND R. A. HOWARD With four plates INTRODUCTION EXTENSIVE INVESTIGATIONS of a wide range of representative dicot-yledons have demonstrated statistically that the structural specializa-tions of the cambium and its derivatives tend in general to progressalong a number of clearly defined lines. Not only are these salientphylogenetic modifications of the cambium and of the secondary xylemmore or less closely correlated, but also at times they synchronize withmorphological specializations of the foliar and floral organs. That theyare significant in discussing the relationships and classification offamilies within certain orders of the dicotyledons has been shown byVestal (9), Tippo (8) and Taylor (7). Extensive exploratory investigations have now progressed to a stagewhere it becomes desirable to initiate intensive studies of specific families.This is essential in obtaining more detailed information regarding therelative rates of morphological specializations in different organs andtissues, in determining which trends of specialization are irreversible,and in securing clues regarding the actual significance of anatomicalcriteria in discussions concerning specific, generic and tribal relationships. GENERAL PLAN OF PROCEDURE In the case of most families of the dicotyledons, two types of materialonly are available at present for morphological and anatomical investi-gations, viz. (1) herbarium specimens and (2) the collections of woodsassembled at Yale, Oxford and Harvard Universities and at other insti-tutions. It is evident, accordingly, that in initiating an intensive studyof a particular family, it is necessary to focus one's attention largelyupon the secondary xylem and upon such tissues and organs as areadequately preserved in ordinary herbarium specimens, i.e. slenderstems, leaves and flowers. Our investigations of the Icacinaceae will deal successively with thegross anatomy of the node and internode, the histology of the tracheary
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