- uptake of water by roots.
- movement of water through plants, mainly through xylem
- loss of water vapor from leaves and other above ground plant parts;
mainly occurs through the stomata.
- loss of liquid water from leaves;
occurs through hydathodes
to stomata, but they do not close).
OF WATER ABSORPTION
roots - most absorption, mainly through root hairs due to:
very numerous - 14 billion on a typical rye plant.
large surface area -14,000 ft2 (1310 m2) on a typical
and constantly produced - 975 linear ft (300 m) per day on a squash plant
roots - little absorption due to:
suberization of endodermis
periderm (bark) formation
THEORY OF TRANSLOCATION IN THE XYLEM
occurs and is driving force
2) Causes negative
pressure in leaves
of water is pulled up in the xylem and translocated due to:
a) H-bonding (hydrogen-bonding)
b) small size of xylem pores
charges on xylem walls
force for translocation: transpiration causes a negative pressure
which "pulls" the water up the xylem.
cooling of leaves: 540 cal of heat energy is dissipated
for every gram
of water that evaporates from leaves, which is a major contributor to the
Transpiration is usually
much greater than is needed to satisfy these two functions. Thus, many
horticultural practices attempt to minimize excessive transpiration.