Grasses don’t have large showy flowers. Instead, the flowers
are usually small and fairly insignificant, until gathered together
as an inflorescence raised clear of the foliage. Then they show
the diversity of form and size that has made them so popular as
garden ornamentals – the tassels of Miscanthus sinensis,
the dense columnar spikes of Pennisetum alopecuroides and
the delicately branched panicles of quaking grass (Briza).
Blowing in the wind
At the height of the hayfever season, sufferers are acutely aware
of the vast quantities of pollen that grasses release into the air.
Grass flowers themselves consist of little more than three pollen-producing
stamens and an ovary bearing two pollen-capturing stigmas. Two sets
of thin scales protect the flowers. Each grass flower is enclosed
in one pair of scales (lemma and palea), forming a floret. A spikelet
consists of a second pair of protective scales, the glumes, surrounding
one or more florets. When the florets open, the scales part so that
the stamens and the feathery stigmas are exposed to take advantage
of the slightest breath of wind. Once a floret’s pollen has
been dispersed, its stigmas become receptive as they intercept pollen
grains blowing past. This ensures that the florets are cross pollinated.
A single maize plant can produce over 14 million grains of pollen.
All wrapped up
Cereals and other grasses carefully safeguard their developing
seeds, by enclosing them within several different protective layers.
Reaching the starchy kernel of a grain of rice is rather like unwrapping
a parcel. The outer husk or chaff consists of various dry scales
that originally protected the flower. Once these have been removed
by threshing and winnowing, the product is brown rice. Next the
rice is milled to detach the bran, made up of the outer fruit wall
fused with the inner seed coat. The final stage is the removal of
the germ (the seed’s embryo) together with a protein-rich
aleurone layer which helps to release the sugars needed during germination. White rice itself
represents the seed’s starch reserve. This supports the
embryo’s early growth until its own green leaves
begin to produce food by photosynthesis.
Children fed solely on white rice can suffer from the vitamin deficiency
beri-beri. Vitamins are lost as the bran and germ are removed. |
