Silica Distribution in Equisetum Hyemale Var. Affine L. (Engelm) in Relation to the Negative Geotropic Response

Summary In young growing Equisetum shoots silica deposition proceeds basipetally in the internodes. The surface of the mature internode, including the stomata, becomes encrusted with silica. Only young shoots with active intercalary meristems and very little silica deposition show a negative geotropic response. As the internodes mature, the difference in silica deposition between intercalary meristem and upper part diminishes so that the failure of mature internodes to respond geotropically is most likely due to significant silica deposition in the once active intercalary meristem sites. Initiation of negative geotropic curvature in young Equisetum shoots takes 36 to 48 h, and six to nine internodes are involved. Control of the geotropic response is auxin‐mediated as shown by experiments with the auxin transport inhibitors, triiodobenzoic acid (TIBA) and methyl‐2‐chloro‐9‐hydroxy fluorene (CFM, a morphactin). The former partially inhibited the response while the latter completely inhibited curvature.