BAKER, DAVID M. c/o Donald Kaplan, Department of Plant Biology, 111 Koshland Hall, University of California, Berkeley CA 94720-3102. - Stipules and shoot development of Exbucklandia populnea.
Leaves of Exbucklandia populnea (Hamamelidaceae) bear a large,
leathery, persistent structure at the base of their petioles which
encloses the next youngest leaves produced by its shoot. By means of
electron micrographs and serial sections, it was determined that the
structure is formed by the appression of two lateral stipules. Such
stipular morphology, but in a less elaborated form, also occurs in the
infloresence region. During a vegetative flush, between one and four
branches expand out from between the stipules. The origin of these
branch buds within the stipular bud was studied to determine whether
they arise as either collateral axillary buds or from a condensed
branching system. The phyllotaxis and plastochron of leaves borne on
these shoots was determined; rates of growth of these shoots during
their subsequent expansion was studied and compared in relative and
absolute terms. The significance of these observations for an
understanding of tree architecture will be discussed.
Key words: Exbucklandia populnea, Hamamelidaceae, scanning electron microscope, shoot branching, stipules