3.1: Background

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Now that you are familiar with the scientific method, it is time to practice using it in a laboratory setting. Let us start with the sensitive plant, Mimosa pudica.

Mimosa pudica is a short-lived sub-shrub that is native to Brazil, but has become pan-tropical. It has prickly stems that can grow to a height and spread of about one meter. In some areas, it is considered a noxious weed. Mimosa can grow in most well-drained soils regardless of nutrient content, but it is not shade tolerant. As a member of the bean family, Leguminosae, Mimosa roots contain nitrogen-fixing nodules. In cultivation, Mimosa will produce pink, fluffy from multiple stamens flowers from which viable seeds may be collected. All parts of the plant are toxic, and should not be ingested. As you see, plant is well-defended, even roots (after the touch) have strong garlic odor which repels soil animals.

Mimosa pudica is commonly called the sensitive plant, as it responds to stimulus. Yes, it moves. Of course, most plants move to some extent (like young sunflowers twisting to face the sun all day), but Mimosa actually retracts from stimuli! The response of Mimosa pudica to seismic stimulus is immediate and captures the attention of anyone observing it. Even Charles Darwin was intrigued enough to devote time to describing the leaf-closing response of this plant to external stimuli.

Note that plants recover best under the bright light.

In addition to Mimosa pudica, you might also have today couple of plants of Biophytum sensitivum, another sensitive plant of Asian origin, from wood sorrel family, Oxalidaceae. This one also reacts to stimuli, but not exactly like Mimosa. You can use it to answer the last question.