Using Cress in the Lab

Cress seeds are cheap and easy to grow, and offer a useful way to look at the germination process and the many factors that can affect it.  As such, they’re frequently recommended in  biology specifications and used by many schools. White mustard (Sinapsis alba) seeds make a useful alternative in these practicals, being frequently cheaper and easier to handle, and slightly more reliable in germination.

Practicals

• Plant growth: Resource: Explore whether cress seedlings grow towards light
• Plant growth: Resource: A simple protocol for investigating seed germination
• DNA: Cress and other brassicas are suitable for the SAPS / NCBE PCR technique, and can be contrasted with spider plants. Resource: Investigating plant evolution with the SAPS / NCBE PCR kit
• Student project idea: Do tomato extracts inhibit the germination of cress seeds?
• Student project idea: Selecting plants for growth studies
• Student project idea: The effect of heavy metal chlorides on cress seedlings
• Plant growth: Idea: Investigate the effect of water on germinating seedlings (following the protocol above)
• Effects of pollution: Idea: Investigate the germination of seeds and growth of seedlings in different levels of acid rain (following the protocol above)
• Photosynthesis: Investigating the behaviour of leaf discs

Teaching Topics

• Effects of Pollution
• Plant Growth
• Plant Nutrition

Description

Cress, Lepidium sativum

Commonly grown in England as a salad crop with mustard (Sinapsis alba). The two together will be familiar as the ‘mustard and cress’ found in egg sandwiches. Cress is a member of the Brassicaceae family, as are radishes and beetroot.

Cress is generally quick and reliable to germinate, which makes it a useful choice for experiments looking at the germination process and factors that affect it, such as pollution. However, it is always worth considering the use of white mustard (Sinapsis alba) seeds instead, as they are frequently cheaper, are easier to handle, do not have the distinct odour of cress, and their germination has been found to be more reliable in schools.

Note that ‘cress’ sold in a supermarket is not necessarily Lepidium sativum: it is often another brassica, such as white mustard or oil seed rape. These are still suitable for use in the ‘photosynthesis with leaf discs’ experiment.

Growing and sourcing

Obtaining: All the main seed suppliers stock this plant, as do Blades Biological. Each seed pack contains around 1,000 seeds providing an economical source of quick growing, tiny plants for a wide range of classroom investigations.

Propagating: An excellent, inexpensive plant easily grown from very small, red-brown seeds. Each seed has deep, three-lobed cotyledons and takes between 10-14 days to grow.

Compost: Damp cotton wool or filter paper provides an ideal growing medium as does damp paper towel. You can use petri dishes in a modified plastic bottle.

Light: Keep the seeds dark until after germination and then move to a warm well-lit spot making sure the growing surface stays moist.

Water: Keep damp without soaking.

Temperature: Keep in room temperature.

Feeding: There is no need to feed these seedlings.

Notes: Look out for signs of ‘Damping-off” in your seedlings.