On A Geo-Growth Reaction of the Avena Coleoptile

The growth of Avena coleoptiles during a period of 5%-7 hours in which they carry out two geotropic curvatures (in opposite directions), and finally are allowed to straighten out, remains behind that of coleoptiles in the normal vertical position. This is true for non-decapitated coleoptiles in water, and for decapitated ones in a 0.05 mg/1 IAA solution. The decreased growth of curving coleoptiles is not due to the bending, since the same reduction is observed when horizontal coleoptiles are prevented from curving geotropically by reversing them every ten minutes. The above retardation was not found in the 0.1 mg/1 IAA solution. A gravity-induced decrease of the auxin transport is proposed as a possible explanation of the retarded growth of horizontal coleoptiles.