Pharmaceutical botany - Lighthouse Survival Blog

THE LEAF 31
The leaf of the Tulip Poplar or Liriodendron affords a good example
of a Complete Leaf.
Sometimes the lamina or blade is attached directly to the stem
by its base and is then said to be sessile. If the petiole is present,
petiolate.
When leaf stipules are absent, the leaf is said to be exstipulate,
when present, stipulate.
The petiole is seldom cylindrical in form, but usually channelled
Fig. 25.—Stereogram of leaf structure. Part of a veinlet is shown on the right.
Intercellular spaces are shaded. {From Steiens.)
on the upper side, flattened, or compressed. The stipules are always
in pairs and closely resemble the leaf in structure.
The blade of the leaf consists of the framework, made up of branching
vessels of the petiole, which are woody tubes pervading the soft tissue
called mesophyll, or leaf parenchyme, and serve not only as supports
but as veins to conduct nutritive fluids. Veins are absent in simple
leaves such as many of the Mosses.
Leaf Venation.—Furcate or Forked Venation is characteristic
of many Cryptogams.