Download SPECIALIZED/MODIFIED STEMS Stems may be of various forms to

SPECIALIZED/MODIFIED STEMS
  Stems
may be of various forms to serve different
functions, such as for food or water storage, for
subterranean or aerial anchoring devices, as a means of
asexual reproduction, or for climbing.
SPECIALIZED/MODIFIED STEMS
  Bulbs
– A bulb is a short, underground, food-storage
stem axis with extremely reduced internodes and
surrounding fleshy scale leaves (a). An onion is the
example.
  Corm – A solid, bulb-like , underground stem without
fleshy scales forms a corm. It has greatly shortened
internodes. Examples are the food-storage, reproductive
corms of Gladiolus and Crocus.
SPECIALIZED/MODIFIED STEMS
 Pseudobulb
– Many
orchids grow on
branches or trunks of
other plants
(epiphytes). These
plants develop a fleshy
stem internode with
water storage
parenchyma. Other
orchids, in contrast,
are terrestrial (grow in
the soil).
SPECIALIZED/MODIFIED STEMS
 Rhizome
– Found
near or below the soil
surface, a rhizome is
an underground stem
that produces scalelike leaves and
adventitious roots at
the nodes. Rhizomes
are found in Iris,
Equisetum, and Irish
potatoes.
SPECIALIZED/MODIFIED STEMS
 Stolon
– A lateral stem,
“runner”, from the base
of a plant develops
internodes, and where
the apex touches the
soil, a new plant with
shoots and adventitious
roots forms at a node.
Strawberry and
strawberry begonia
form stolons.
SPECIALIZED/MODIFIED STEMS
 Succulent
stem/
cladophyll – Fleshy
water storage stems
of parenchyma are
found in the spurge
and cactus families.
In prickly pear cacti,
nodes bear leaves
that have been
reduced to spines.
SPECIALIZED/MODIFIED STEMS
 Tuber
– Tubers are
swollen,
underground good
storage stems arising
at the tips of
rhizomes. They bear
buds, ”eyes”, at the
nodes on the potato
tuber. These “eyes”
develop into potato
sprouts (shoots)
when the potato
starts to grow.
SPECIALIZED/MODIFIED STEMS
  Vine
– Vines are stems with long internodes and
may have one of various types of climbing devices
such as tendrils opposite leaves at a node as in
grape, modified stipule tendrils (w) as in green
briar, disc-tipped tendrils (t) as in Virginia
Creeper, adventitious roots as in philodendron
and ivy (q), twining leaf tips as in gloriosa lily,
and twining lea petioles as in clematis, or the
entire vine may twine as in wood rose.
WOOD AND ITS USES
  In
a living tree, 50% of the wood weight comes
from water content.
  Dry weight is composed of 60-75% cellulose
and 15-25% lignin.
  Density and Durability are two of the most
important characteristics in commercial wood.
WOOD AND ITS USES
 Sawing
  Radially
cut (quartersawed) boards
show the annual rings in a side view.
  Tangentially cut (plain-sawed) boards
show annual rings as irregular bands of
light and dark streaks.
WOOD AND ITS USES
 Knots
  Bases
of lost branches covered by new
annual rings produced by the
cambium of the trunk.
  Found in greater concentration in
older parts of the log, towards the
center.
WOOD AND ITS USES
  Wood
Products
  About half of US and Canadian wood
production is used as lumber, primarily for
construction.
 Veneer - Thin sheet of desirable wood glued
to cheaper lumber.
  Second most extensive use of wood is pulp.
  In developing countries, approximately half of
cut timber is used for fuel.
 Less than 10% in US and Canada.
REVIEW
  External
Form of a Woody Twig
  Stem Origin and Development
  Stem Tissue Patterns
  Herbaceous Dicotyledonous Stems
  Woody Dicotyledonous Stems
  Monocotyledonous Stems
  Specialized Stems
  Wood and Its Uses
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