across a stalk of Indian Corn ;• these stems are called Endogenous or
Endogens, (inside growers). The terms Dicotyledonous and Exogenous
are used synonymously, as are Monocotyledonous and Endogenous.
20. The Leaf. It is in the leaf that the important work of trans-
forming the crude sap, which is taken up by the roots, into organized
material fit to enter into the growth of the plant, is performed. In this

Erocess the agency of sunlight is required and a free exposure to the air,
ence the leaves are so made and so disposed upon the stem as to present
the greatest possible surface to these influences. A leaf, having all its
parte, consists of an expanded portion, (the Blades Lamiruiy or Limh) a
stalk by which it is attached to the stem, (the Petiole or Leaf-stalk,) and
a pair of appendages at the base of the leaf-stalk, called Stipules. The
petiole and stipules may one or both be absent, the essential portion
being the blade. Leaves having a petiole are said to be vetioled or pe-
tiolate ; without a petiole they are sessile. Where the blade joins the
petiole, or, if this be absent, the stem, is ite kase ; the opposite ends are
the apexy and the sides are liie margins.
