IT CONSISTS A BRIEF INTRODUCTION TO GYMNOSPERMS. ANATOMY OF GYMNOSPERMIC WOOD IS DISCUSSED BRIEFLY.

1. GYMNOSPERMIC
WOOD

2. Gymnosperms
 Gymnosperms are an intriguing group
of plants.
 There are four groups gymnosperms:
 Conifers
 Cycads
 Ginkgo
 Gnetales
These groups are so different from each
other in most of the features.

3.  The most common feature across all four groups is
that the ovule (which becomes the seed) is naked
(unprotected) prior to fertilization. In comparison, the
angiosperms have ovules that are protected by a layer
of tissue called a carpel.
 The word gymnosperm comes from ancient greek and
means “naked seed.” This naked state of the ovule is
a unifying feature of the gymnosperms

4. Cycads
 Cycads are a very ancient lineage of plants with a
fossil record that extends back at least 280 million
years.
 Cycads are dioecious, meaning that there are
separate male plants that produce pollen cones and
female plants that produce seed cones.
 The cones of cycads are typically large.

5. Ginkgo
 Ginkgo biloba is the sole living species of the
once widely distributed order ginkgo ales
and is often called a “living fossil”.
 The male pollen cones (strobili) are simple
structures that arise at the base of leaves on
the short shoots.
 Female cones (strobili) also arise at the base
of leaves on the short shoots and consist of a
stalk and two terminal ovules.

6. Conifers
 Conifers are the most conspicuous group of
gymnosperms, containing 7 families and
more than 600 species.
 They tend to dominate forests in the
northern hemisphere and have a rich and
diverse existence in the southern
hemisphere, but are reduced in numbers in
most tropical environments.

7. Continued…
 The pollen cones of conifers are always
simple.
 All living conifers are woody plants, and
most are trees.
 Many conifers have distinctly scented
resin, secreted to protect the tree against
insect infestation and fungal infection of
wounds.

8. Gnetales
 The gnetales are the most enigmatic group
of the gymnosperms.
 This order of plants is made up of 3 families
 Ephedraceae
 Gnetaceae
 welwitschiaceae—each with a single genus.

9. Anatomy of ginkgo
 To understand the anatomy of
gymnospermic wood we are
taking here the example of the
wood of ginkgo

10. Stem
 The young stem (long shoot) is more or less circular
in outline and remains surrounded by a single-
layered, thickly circularized epidermis (fig. 10.9) made
of brick-shaped cells.
 Epidermis is replaced by periderm in the older stems.
 Inner to the epidermal layer is present a well-marked
region of parenchymatous cortex.

11. Continued…
 Cortex is comparatively less extensive in long shoots than
dwarf shoots.
 Endodermis and pericycle are not well-marked in long
shoot.
 Several conjoint, collateral, open and endarch vascular
bundles are arranged in a ring in very young stem.

12. Continued…
 Two leaf traces, one for each leaf, are given
out.
 Protoxylem has spiral thickenings while
bordered pits are present on the radial walls
of the metaxylem tracheids.
 Sieve tubes and phloem parenchyma
constitute the phloem.

13. Secondary growth in stem:
 Cork cambium cuts periderm towards outer
side and secondary cortex towards inner side
(fig. 10.10).
 Periderm replaces the epidermis.
 Mucilage canals are absent.

14.  A single ring of cambium remains active
throughout and cuts secondary phloem
towards outer side and secondary xylem
towards inner side.
 Crushed patches of primary phloem towards
outer side and primary xylem towards inner
side are present.
 Secondary phloem consists of sieve tubes
and phloem parenchyma.
 Secondary xylem consists of tracheid.

15.  One or two rows of bordered pits are present on the radial
walls of the tracheids (fig. 10.13).
 Pits are circular in outline.
 Bars of sanio are also present.
 Bars of sanio do not occur in primary wood.