Caryopses with primary roots ofZea maysL. (cv. Golden Cross Bantam 70) were incubated on agar-solidified distilled water (0.4%agar) in a magnetic field of 5 k gauss or 0.01 k gauss (control), the direction of root growth corresponding to the direction of magnetic field from the north- to the south-seeking pole. The rate of growth of the roots exposed to 5 k gauss was increased by about 25%over that of the controls (0.01 k gauss). When caryopses with primary roots were incubated on agar-solidified distilled water that had previously been exposed to a magnetic field of 5 k gauss or 0.01 k gauss, no differences in rates of root growth were observed. The growth rate of the primary root increased with increased magnetic flux density (from 0.01 k to 5 k gauss). The orientation of the root in terms of the direction of the magnetic field (from the north- to the south-seeking pole) affected the rate of growth of the root. When the direction of root growth was in line with the direction of the magnetic field of 5 k gauss or in the direction opposite to that of the field, growth rates increased by 27%and 22%, respectively, of the growth rate of the controls (magnetic field of 0.01 k gauss). When the direction of growth was perpendicular to the direction the field, the growth rate increased by 15%of that of the control (0.01 k gauss). It appears that a magnetic stimulus may induce an increase in the rate of root growth in some plant materials.
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