Gravity-induced cell elongation.

When the flowering stalks of grasses are displaced from the vertical position they are caused to bend at special gravity perceptive regions, the nodes. Growth of the lower side of the node returns the shoot to its original orientation with respect to gravity, but when this is achieved, growth ceases. Possible mechanisms by which elongation growth is turned on in the lower sides and turned off again once the stalk is vertical are described. The facilities of Spacelab offer a unique opportunity for testing models of gravity perception and response.