title: Apical involvement in geogrowth responses of the horizontal hypocotyl.
abstract: Hypocotyls of horizontal sunflower (Helianthus annuus L.) seedlings grow more than those of vertical seedlings during the 24 h period following geostimulus. The major contribution to this increased growth arises from extension in the basal half of the geostimulated hypocotyls. H seedling hypocotyls are flexed to a right angle so that the apical half is vertical and the basal half is horizontal, the growth rate of the basal half is similar to that of a vertical hypocotyl rather than a horizontal hypocotyl. These results are taken as indicating that the georesponse of the basal half is not independent of the apical half. It is concluded that the apical region exercises a co-ordinating role in the overall response of the hypocotyl to geostimulation.
authors.affiliation: The Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen AB9 2QJ U.K.
authors.forename: I R
authors.initials: IR
authors.lastname: Macdonald
authors.forename: J W
authors.initials: JW
authors.lastname: Hart