Results
Observations
First study
Almost none of the plants of the first series on the clinostat did germinate, although the plants next to the clinostat did (see figure 5).
Figure 5. The growth of the plants on the clinostat, the first series.
|
|
The longer the plants had been growing in normal conditions previously, the better they continued germinating on the clinostat (see figures 6 and 7).
Figure 6. The growth of the plants on the clinostat: Plants having grown in normal conditions during four days prior to the experiment.
|
|
The plants 1-8 are controls, the plants A-H are the plants grown on the clinostat.
Figure 7. The growth of the plants on the clinostat: Plants having grown in normal conditions during 7 days prior to the experiment.
|
|
The plants 11-14 are controls, the plants K-N are the plants grown on the clinostat.
However, in all the series, the plants on the clinostat didn't grow as fast as the ones growing in normal conditions, and they tended to become brownish and smooth during a period prior to 10 days (see figures 8, 9, and 10).
Figure 8. Sunflower seedlings grown on the clinostat.
|
|
Figure 9. Pisum sativum seedling grown on the clinostat.
|
|
Figure 10. Cucurbita maxima seedling grown on the clinostat.
|
|
Remark:
The air resistance, as well as the fact that the cotton dried rather quickly, might also explain partly why the plants have more difficulties to germinate and to grow on the clinostat.
Additionally, I studied the germination of cress on the clinostat, at 5,7 m/s2, and I figured out that it grew absolutely normally. The conditions were definitively different for the cress than for the sunflowers. Cress is normally known for a rapid germination, and the gravitational force was higher, but through this test I proved that the fact that the sunflowers failed to germinate properly was not, or at least not only related to the fact of being on the clinostat, or growing in the darkness,.., but that it was mainly related to microgravitropism.
Second study
The second study showed that bean seedlings react normally to a gravity as low as 4 m/s2 . Within 4 hours they managed to bend towards the centre of the wheel (see figure 11).
Figure 11. Bean seedling reacting to a gravity of 4 m/s2.
|
|
Peas (Cicer arietinum) needed 8 hours to bend towards the centre at a gravity of 4 m/s2 . Some sunflower seedlings reacted properly at a gravity of 4,8 m/s2 . However, most of 6,8 m/s2 . At that gravity it took them 5 hours to bend towards the centre of the wheel. Peas (Pisum sativum) needed a gravity of 4,5 m/s2 , pumpkin 5,1 m/s2 , and Soya 8,3 m/s2 in order to bend towards the centre within 4 hours (see figure 12).
Figure 12. Minimal gravity needed by different plants to bend towards the centre of the wheel.
|
|
At a gravity below the minimum, the plants became smooth and brownish, and they bent into any direction.
At a gravity above the minimum, the plants grew normally (= with the stem oriented towards the centre of the wheel).
Interpretation
The first study showed that a lowering of the gravity is actually taken into account by sunflowers. It slows down or even stops germination. It seems that, the longer the seedlings previously germinate in normal conditions, the better they can cope with a low gravity.
The second study showed the sensibility of the different plants to a low gravity. It seems that plants with larger stems (e.g. beans) can cope with a lower gravity than the other plants (e.g. Soya, cress) do.
Surprisingly, cress germinates better than sunflowers under the effects of microgravitropism (see the first study), but once it has germinated, it requires a higher gravity than the other plants do in order to bend properly. This may be explained by the characteristics of cress: it germinates fast and easily (even in water without having any support, e.g. in rivers), but the seedlings are very fragile.
