2. CONDUCTION OF MATERIALS BY
STEMS
Conduction by Xylem
Chief function of xylem is the
upward conduction of water and
dissolved substances (sap). These
dissolved substances are chiefly mineral
salts from the soil; also, foods previously
stored in the roots and stem may be
conducted upward in spring in woody
plants.
3. Ascents of Saps
Root Pressure
This explains the exudation of sap
from the stumps of decapitated or
detopped plants including those of
trees that were newly felled.
4. Capillary Attraction
1)water rises in narrow tubes due to the
force of surface tension
• It stated that it is the capillary action of
narrow xylem tubes and it is further
supported by atmospheric pressure
6. Action of Living Cells
Suggested that living cells
adjoining the conduction cells of
the xylem force water upward,
possibly by some sort of pumping
action.
7. Imbibition in Cell Walls of Xylem
The cell walls of xylem cells
absorb water ny imbibition, but
imbibitional force is not sufficient to
explain either the rapidity or
magnitude of sap rise.
8. Transpiration Pull and Water
Cohesion
This explains that the upward movement of
water is mainly due to the creation of a negative
force or tension attributed to the continuous
evaporation of water at the surfaces of leaves in
the process of transpiration. As molecule after
molecule of water evaporates through the
stomata, it creates a pulling action on the next
molecules of water in the transpiration stream.
9. The transpiration pull is similar to the
suction force when drinking some
fluid from a bottle or glass with a
straw. Water can also be sucked into
a pippette with the use of an
ordinary rubber aspirator or with a
common medicine dropper.
10. Conduction by Phloem
The chief evidence of phloem is the
downward conduction of foods
manufactured in the leaves.
Some upward conduction of
minerals and foods occurs in the
phloem.
11. Conduction of Vascular Rays
In which extend ought
radially in stems extend through
the xylem and also into the
phloem. These rays bring about
the transverAse (crosswise)
conduction of foods, minerals,
water, and gases.
12. Other Functions of stems
Food Storage
Occurs chiefly in the parenchyma cells
of cortex, rays, and pith, and also in the
phloem and xylem parenchyma.
Climbing stems
Tendrils, such as those of grapes, or
twining stems such as those of morning
glories, are examples.
13. Food Manufacture
stems ehich contain chlorophyll, such as
those of most herbaceous plants and of cacti,
manufacture food.
Reproduction
Production is brought about by
runners, by the branching rhizomes , by the
formation of new bulbs and corns from older
ones, etc.
14. PRACTICAL APPLICATIONS OF A
KNOWLEDGE OF STEM STRUCTURE AND
PHYSIOLOGY
PRUNING
In pruning away diseased , broken
or otherwise undesired branch, the cut
should be made as close to the main
branch as parallel to i, in order that the
growth tissues sorrounding the wound
may form new tissues to heal the
wound.
15. GIRDLING
Is the removal of a complete ring of
bark . Girdling stops the downward passage
of food, which collects above the girdle.
Practiced in order to;
1. Produce large fruits
2. Kill trees, in clearing land.
3.Produce more flowersin the season
following girdle.
16. GRAFTING
Is a horticultural practice in
which two freshly cut stem
surfaces are bound together in
such fashion that their cells
grow together; thus there is
formeda union between the two
pieces of stem.
