Figure 6.

A pHc gradient is set up across tier 2 immediately following gravistimulation (t = 0 s), whereas there is no gradient across tier 3. A, Tier 2 shows a delay in the onset of alkalinization of the upper cells (●) compared with the lower cells (▿) by approximately 100 s, establishing a gradient across tier 2. B, The timing of the acidification of tier 3 is similar in upper (●) and lower (▿) cells following gravistimulation. Gravistimulation occurs at t = 0 s (n = 10). Error bars are not shown for clarity, but are approximately ±0.2 pH unit.