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Investigations on the Phylogeny of the Angiosperms. 3. Nodal Anatomy and the Morphology of Stipules

Edmund W. Sinnott and Irving W. Bailey
American Journal of Botany
Vol. 1, No. 9 (Nov., 1914), pp. 441-453
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Page Count: 14
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I. There is an intimate connection between the type of nodal anatomy (one, three or many traces and gaps) and the occurrence of stipules and similar structures in dicotyledons. In the majority of plants with a trilacunar node stipules are present; in almost all with a unilacunar node they are absent, and in all with a multilacunar node the leaf has a sheathing base. 2. There is a similar connection in monocotyledons, particularly in such primitive forms as the Potamogetonaceae. 3. The growth of the lateral leaf-trace apparently exerts a stimulus which results in the development of the stipule, for the stipule invariably occurs directly opposite the point of departure of the trace. 4. The character of the leaf margin is also important in governing the occurrence of stipules, for stipules are generally absent in entire leaves families, even though the latter are trilacunar. The fact that stipules and leaf teeth almost always possess apical pores or glands which are usually atrophied after the leaf has reached maturity suggests that both structures have essentially the same function. 5. Morphologically, stipules are to be regarded as integral portions of the leaf, and seem to be more nearly homologous with teeth than with any other structures. Stipules, sheaths, ligules and similar modifications of the base of the petiole are dependent in position and character on the anatomy of the node, and seem thus to be essentially homologous. 6. A leat provided with two distinct stipules is more ancient in type than one with a sheating base.