Figure 7.

Determination of the photogravitropic bending angle (γ) as measured on a centrifuge (see “Materials and Methods”). Without unilateral irradiation (hν), the sporangiophore would grow opposite to the resultant (r) of the centrifugal force (c) and the earth gravitational acceleration (g); it would thus be inclined at an angle α above the horizontal centrifuge disc. In the example shown in this figure, the centrifugal acceleration, c, is 4.1g and the resultant, r, is 4.2g. The angle α between c and r is 13.7°. The vector of the unilateral light (hatched line, hν) is perpendicular to r. The angle γ represents the angle of photogravitropic equilibrium. It is determined by subtracting α from the measured bending angle β (protractor reading).