Fig 7. Sporangium motion sequences and spore dissemination.

The sporangia have been gripped at their stalks with tweezers and adjusted vertically. Sporangium 2 in (D) is still situated on a false indusium. ac = apical cup; bc = basal cup; s1 = spores from apical cup; s2 = spores from basal cup. (A) The slow passive nastic movement of the annulus includes rupture of the sporangium (i,ii) and formation of the apical cup and basal cup (iii). The annulus relaxes after this tensioning process (including a first ultrafast relaxation step), but does not immediately reset to its initial position, stopping approximately halfway (iv). Afterwards, the annulus further resets; the extent of this step varies and can lead to a nearly initial annulus curvature, or may stop much earlier. (B) First, ultrafast annulus relaxation step which leads to rapid spore ejection from the apical cup. This step lasts only 40 μs until spores emerge in the respective frame. Afterwards the sporangium bounces and spores from the basal cup also become shed (t = 50–70 μs). Frames were taken from S7 Video, cropped and digitally resized without interpolation. (C) The dissemination pattern during spore ejection from a sporangium is shown. At the beginning, the tensioned annulus is turned in such a way that the apical cup points left backwards. After relaxation, spores of the apical cup are forcibly ejected almost straight downwards, whereas those from the basal cup are shed in an irregular pattern. Frames from S11 Video were cropped and digitally resized without interpolation. (D) Tracked spores from S9 and S10 Videos (images rotated 90° anti-clockwise). Still frames of sporangium 1 and 2 at t = 0, which depict the last frames before the respective annuli start to move, and at t = 0.5 ms respective t = 0.3 ms. The six tracked spores are visible and marked. Spore 5 from the basal cup of sporangium 2 is already visible at t = 0.