Design for cress seed investigation

• The length of the cress seeds

• Controlled

• Nutrients in soil

• The same soil will be used for all different trials, practically the nutrients will decrease faster in the faster growing cress-seeds, however the amount of nutrients should be more than enough due to the relatively low amount of cress seeds (1 cress seed per 17 grams of soil)

• pH of soil

• The same soil will be used for all different trials

• Water

• By using a water spray you can ensure that the water is distributed evenly over all cress seeds, the cress seeds with more light might dry up faster in which case more water will be added.

• Light intensity and wavelength

• The same lamp will be used above all experiments, the distance should be fairly high such that the light can be regarded as a linear light source rather than a radial one.

• Temperature

• All cress-seeds will be in the same room and the lamp should be placed on a sufficient distance such that the temperature of the lamp should not noticably influence the temperature

• Humidity of air

• All cress-seeds will be in the same room

• Carbon dioxide and oxygen concentration

• All cress seeds will be in the same room

• Type and amount of seeds

• All seeds will be of the species Lepidium sativum (garden cress) and each petri dish will contain 5 seeds. Despite a relatively big number of the cress seeds most likely not germinating, the amount of soil available to each seed should be sufficient.

Materials:

• 125x cress seeds
• 20x petri dishes
• 20x 88 cm3 of soil (from a single source) (petri-dishes assumed to have a diameter of 15cm)
• 5x 45*45cm cardboard
• Knife
• Ruler
• Water spray

Method:

1. Take the 5 cardboards and bend 2.5 cm of the sides downwards:

2. Cut the smallest possible holes into each cardboard with the density's described below:

1. (holes not to scale)

3. Fill the petri dishes with the soil
4. Place 5 cress seeds into each petri dish. (Although you should be aware that not all cress-seeds will germinate)
5. Place 4 petri dishes under each cardboard cover
6. Place a single lamp above all the cardboard boxes on a height of approximately 1-2 meter.
7. Measure the height of the cress-seeds every two days for 2 weeks and spray water in such a manner that the humidity of the soil is approximately equal, as the soil under the maximum light might dry up faster.