Dandelions aren't the most obvious resource for a science experiment. However, dandelion flower stalks (scapes) have a strong gravitropic response, and this experiment offers a simple and fun way to look at gravitropism over the course of a double lesson.
If the dandelion scapes are detached from the plant and held sideways for a period of time, they will reorient themselves by bending upwards until they return to a near vertical position. This can be done either as a demonstration, or as individual practicals.
Download full teachers' notes and a student sheet from the links on the right.
Note - when dandelions are out of season, white deadnettles (Lamium album) can be used as an alternative for this experiment. Deadnettles are a widespread weed, found commonly in woodlands, roadsides and waste ground. A useful article in School Science Review reports on this experiment: "Shoots of deadnettle (10 cm long) are stripped of leaves and floral whorls. These are placed horizonatally on tiles with their cut ends supported and surrounded by wet cotton wool. The tiles are then placed in a dark room or cupboard at 200c and examined at 3 hour intervals. Batches of material with apices intact can be compared with batches with the terminal 1-2mm of the shoot removed... The negative geotropism is easily seen within 1-2 hours and readily recorded. The removal of the tip did not prevent the response occurring although it was delayed. The square-shaped stem is easily marked and can be treated with auxin, gibberellic acid etc." (G. S Preece, J. Curthoys and K Taylor, Pershore High School, Worcestershire, 'The use of white deadnettle in geotropic experiments', School Science Review, June 86, pp. 739-741).
