Tanin cells. Change in the mean density of tannin cells along the length of Posidonia oceanica adult leaves (sheaths and blades) as a function of the level of interaction with Caulerpa taxifolia. Distance along the leaf was measured below and above the limit between sheath and blade. For each adult leaf of each shoot several replicates were performed; the total number of replicates was n = 78 (L0) n = 89 (L1), n = 83 (L2). Bars: Confidence level 95%,.