Figure 2: The mean movement per day of 10 short and 10 long
triandra.
Awn Fraser-Pryce was expected to again
leave Florence Griffith-Awner in her dust
on the Green field.
The results were sensational! The long
awns covered > 120 mm more ground than
the short awns during the race (231.3 vs.
110.4 mm), at double the pace (46.3 vs. 22.1
mm day -1 ; Fig. 2). Awnsain Bolt produced a
blistering performance of 122 mm in one
day, completely obliterating the previous
world record of 59 mm (Adams and Tainton
1990).
‘What makes the long ones move so fast?’,
was obviously my next question. Guided
by Francis, I anchored vertical orientated
awns at their base and timed their rotation.
Surprisingly, short and long awns twisted at
the same rate (2 min 48 sec for a complete
rotation), close to what Francis found (2
min 30 sec) and within the range of other
results (2–4 min). According to physics, the
length of the actively twisting basal section
of the awn (which is effectively a torsion
spring) plays no role in determining
how fast it rotates but it, together with the
length of the passive tip of the awn, both
influence how much leverage a bent awn
can exert. Therefore, a long awn will lever
itself more effectively and faster across the
soil than a short awn.
Not content with mere description and
measurement, Francis delved right into the
awn of S. pennata to see what makes it tick.
References
He stripped it down t
noting [that] “under
torsion of the individ
fully seen; ... I have a
cell under the micros
twisting up again as m
and was withdrawn
hood.” He also identi
entially water-absorbe
spiral arrangement o
wall that lead to its
and observed strips o
twist like the whole aw
lular and macro str
that confers torsion
awn movement. All t
well as the whole mac
firmed using the lates
techniques almost 14
and Abraham 2014).
perspicacity and tena
electron microscope d
lockdown, all I manag
veal by way of a blu
first ever) photograph
phone through a ste
the awns of T. triandr
spiral groove in their
(Fig. 1D). How this d
utes to twisting, per
water or acting as a co
ing swelling and shrin
determined.
Of course, you only un
if you can build a wo
1. Adams KM, Tainton NM. 1990. The function of the hygroscopi
Southern Africa 7: 271-273.
2. Darwin F. 1876. On the hygroscopic mechanism by which certa
tions of the Linnean Society of London, 2nd Series. Botany 1:
3. Elbaum R, Abraham Y. 2014. Insights into the microstructures
223: 124-133.
4. Godfree RC, Marshall DJ, Young AG, Miller CH, Mathews S. 2
polyploid advantage in a keystone grass exposed to drought
Grassroots Vol 20 No 2 June 2020