The material

The clinostat is the device used to simulate a low gravity. The clinostat is shown in figures 2a and 2b. The clinostat has been built out of a bicycle. The wheel is rotated by two windscreen-wiper motors. One motor makes the wheel rotate together with the axe of the fork. This helps to eliminate the effects of the Earth's gravitational force. In fact, due to that rotation, one can say that the plants are turned, per period of this single rotation, once upside-down and once upside-up. The other motor makes the wheel turn around the hub (as it normally does).This allows to simulate a new gravitational force. In fact, the centrifugal force resulting from the rotation of the wheel can be compared to a gravitational force that would make the plants grow towards the centre of the wheel. The intensity of the force is proportional to the speed of the wheel, which can be regulated.

- length between the centre of the wheel and the plant: 31 cm

- perimeter: 195 cm

- speed of the rotation around the axe: 5 turns in 55 seconds =0,177 m/s

this speed is not taken into account !

- speed of the rotation around the hub: 10 turns in 17,47 seconds =1,112 m/s

- acceleration of the plants: a=v²/r (v: speed, r: radius) =4,02 m/s² = 0,41 G

- gravitational force: F = m*g, with m = 10 g (weight of the plant in the cotton ball)

The plants

The sunflower seeds (1st. study) / seedlings (2nd study) are put into nylon socks, together with a cotton ball, that keeps the humidity. The socks are fixed onto the spokes of the wheel (see figure 3 and figure 4).

For the first study, I used sunflower seeds (Helianthus annuus).

For the second study, I used sunflower seedlings, and, in order to compare, Soya (Vigna Mungo), peas (Cicer arietinum and Pisum sativum), cress (Lepidium officinale), beans (Phaseolus vulgaris) and pumpkin (Cucurbita maxima).

The seedlings were aged of 12 days when set onto the clinostat.

First study

I started the first study with a series of 10 plants on the clinostat and 10 plants growing in normal conditions, next to the clinostat. First, the seeds where placed during one night into water. Then, they were fixed onto the wheel as explained above. The acceleration of the plants was equal to 4,02 m/s². The room temperature was 21⁰ C, and the room was darkened to eliminate phototropic effects. The plants had to be wetted very frequently, for the cotton dried quickly. The plants were measured and analysed once a day. The study lasted 15 days.

As the plants on the clinostat hadn't managed to germinate, I repeated the study with other series of plants that had previously been germinating in normal conditions for 7, respectively 6, and 4 days.

For each series, at the beginning of the study on the clinostat, the size of the plants on the clinostat matched in pairs with the size of the plants growing next to the clinostat.

As those plants reacted faster, the study period for series 2, 3, and 4 was shorter than for series 1.

Second study

The seedlings were also put into nylon socks, with the stem passing through a small hole (see figure 3).The speed of the wheel varied for each series. Each series was composed of several samples of each type of plant studied (sunflower, peas, Soya, beans, pumpkin, cress).

For every new series, the speed of the wheel became more important.

The period of one series lasted either until the plants had managed to bend towards the centre of the wheel (this was the signal that they could perceive the gravitational force), or until the plants were completely broken, smoothened or perished, or until a certain condition might be fulfilled that was still ignored at the beginning of the study (e.g. that the plants would grow in a specific way, which would characterise the plants' microgravitropic response).

If a type of plants failed to grow on the clinostat (case 2 listed above), some new seedlings of that type were used in the following series, at a higher gravitational force, until, finally, the minimum speed for the plant to bend properly, was reached.

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