A storage
organ is any
part of the plant in which excess of energy (generally in the
form of starch,
sugars,
lipids or
protein),
nutrients
or water are
stored in order to be used for future
growth
(usually in
biennial or
perennial plants). In the first year
biomass is
added to the storage organ. Afterwards
some of the biomass from the storage organ is returned to the
rest of the plant.
Storage organs often grow
underground,
where they are better protected from
attack by
herbivores. Underground storage organs are also
characteristic of
geophytes.
They evolved as a mechanism for plant
survival through adverse
climatic
conditions, and as a result, geophytes in their natural
habitats
are capable of
perennial
life cycles.
In the geophyte - especially during
temperature
extremes and prolonged
drought -
the aerial
portions die
back, leaving only the storage organ in the
soil until the temperature or
water availability is appropriate for
above-ground growth. This
stage in geophyte
development
is often referred to as a
dormancy period or resting stage. But the storage organ is
never
physiologically dormant even when aerial growth is halted.
It continues to change and constantly
senses its
environment
like a biocomputer.
In common parlance, underground
storage organs may be generically called
roots,
tubers, or
bulbs, but to
the botanist
these are specific,
technical terms, which apply only more narrowly:
In some plants the storage organ
are short-lived and
serve as
regenerative organ bearing a
bud or buds
(e.g. a tuber); in that case the plant dies back in the
resting
season, except for the underground storage organ with the
buds, later utilised for
regrowth;
afterwards old tubers
decay and new
ones are formed. In addition some plants produce smaller
reproductive storage organs (bulbils,
small tubers, etc); plants growing from them resemble in
morphology
and size seedlings. |
